I didn't really write much on military theory topics for a while, and that's a mistake.
My military theory-tagged writings are a mix of some appreciation for old insights and practices, some peripheral topics and my core interest: How to deter / prepare for / wage a land warfare campaign as defending ("war of necessity") power or bloc in a land/air campaign. This is about a clash mostly between great powers. The kind of warfare that made Europe so fearsome militarily and broke much of it twice. Hence a healthy emphasis on "to deter".
There's nothing to be gained in such a war. Whatever you take or force on others, you'll pay way too much for it. The only sensible choice is to get over with it quickly, and with an acceptable outcome.
This means the defending power(s) should visibly gain the upper hand quickly, and proceed to offer a quick, face-saving and relatively cheap status quo ante peace or at least an armistice.
Any pondering about how to occupy the aggressor's countryside is thus moot. Very subtle progress in warfare isn't very helpful. Escalation - especially involving additional powers or introducing nuclear weapons - could prove to be perverse. To knock out the aggressor's government only keeps the aggressor from negotiating, and is thus counter-productive.
Highly visible and credible strength is fine for deterrence, but only if it is not so great that it creates fear of invasion and only if the strength is actually applicable: It doesn't help to know multiple divisions will arrive in two months if the aggressor intends a limited coup de main followed by a peace offer only.
The differences between textbook approach and reality will vary. Sometimes it will work almost flawlessly, other times a unit may be 50% understrength, lack radio comm, be low on supplies and tired. An all-round strong military has to at least potentially be good under all circumstances. You need to be able to exploit when and where you have superior power. You need to bee able to accomplish modestly ambitious missions with little resources. You need to avoid paralysis or collapse during a crisis.
Versatility, ability to function as fragments, ability to make do with a fraction of authorized strength ... there are many highly unfashionable and unsympathetic topics which deserve at least as much attention as the shiny new tool and its music-supported CGI video advertisement.
Infantry manoeuvred and fought in units of hundreds of men for thousands of years. The firepower revolution of the 'smokeless' powders changed this. Theoreticians understood that infantry would need to exploit cover and concealment during the approach in order to survive this firepower until it's close to the enemy. They did not figure out that this necessitated manoeuvre and combat in at most platoon-sized elements because cover and concealment were in short supply (nor did they figure out how to overcome defenders on the last few hundred metres). Practicians had to figure this out in 1914-1916.
Infantry adapted; by WW2 army offensives on cluttered terrain (such as in Italy) were really a string of platoon engagements.
It is likely that mechanized forces still need to transition to a fully developed model for small manoeuvre unit tactics, leaving the big manoeuvre unit approach to engagements under very favourable circumstances only. Tank companies and platoons can and often do manoeuvre independently, of course - especially in battlefield reconnaissance and security missions. I'm somewhat ambitious and believe that this is far from "fully developed model for small manoeuvre unit tactics", and this is in part a matter of equipment versatility.
The challenge is about the same on the tactical level as on the strategic level; it's of lesser interest what to do on the battlefield when local superiority has been achieved. It's also of lesser interest how a clash between two largely intact and capable forces would end.
What's most interesting is how to shape the battlefield, how to create advantages prior to the main clash - or rather without a really big clash.
The focus should be on how to create advantages prior to the big clash, not during the big clash. A brilliant manoeuvre in the midst of a battle when thousands were already sent into the meatgrinder is fine for history books, but it's very, very late.
Small unit manoeuvre tactics and the reconnaissance's principle of committing few to high risks in order to alleviate the risks for the majority of the force are likely able to help very much.
Schwerpunkt. The current interpretations of "Schwerpunkt" vary a lot and are being applied to many different topics. The nature and validity of a Schwerpunkt is very different on the bloc, corps, brigade and battalion levels. Schwerpunkt / Economy of force and similar concepts are self-evident and valid ideas which help to avoid wasteful behaviour. The interpretations which obsess about the enemy's Schwerpunkt meanwhile cannot really show a track record of usefulness in real warfare.
Schwerpunkt is valid inasmuch as it helps us to maintain self-discipline and clarity of thought at times; it keeps us from fizzling out and demands a better husbanding of resources.
I do not fully subscribe to the concept, though. As mentioned in (4), the challenge is to prepare for tactical victory by accumulating advantages. The husbanding of resources as advised by the Schwerpunkt concept is but one way of many how to do this, and not ranking particularly highly amongst them. Too much attention to the Schwerpunkt can lead to ponderous preparations and risky bunching up of forces. Moreover, a fixation on the "bigger battalions win battles" school of thought keeps us from looking at the important micro level of independently manoeuvring small units and units or the value of shaping operations.
Answers depend on questions, military theory answers depend on circumstances. A force which is meant to handle a conflict quickly and satisfactorily will likely not be able to do so with the full power of its bloc. In fact, leaving much if not most of the bloc's power out of the campaign may allow their power to serve as bargaining chips in negotiations. You cannot threaten to add forces into the fray any more if you already did it. Few things impress as much in battle as the arrival and intervention of reinforcements, and politicians are likely to feel the anxiousness about this as well.
A conflict may thus be not only limited in time (quick) and geography (no escalation), but also very much limited in the forces committed. The consequence would be a rather low ratio of forces to terrain during the first weeks. This is even more important as fully motorized forces may move a lot, and may be positioned in great depth (thus increasing the area).
The battlefield may not only seem to be empty; it may actually be quite empty. Really defensible lines are not to be expected unless the geography really favours this. We have actually never seen a land campaign between two competent and fully motorized great power forces. The campaigns of Israel faced moderately competent forces and demonstrated a remarkable instability and record-breaking destructiveness. This was repeated against Iraqis, but this may prove to be no more instructive for campaigns against competents than was mowing down tribal spearmen with Maxim machineguns.
Conflict scenarios and musings of people who stick more to a conquest-like idea of war are bound to produce different conclusions.