The EU and European NATO are vastly more powerful than all non-allied neighbours combined, even if we would count Switzerland and NATO ally Turkey against the EU, for example. Russia doesn't come close to the sum of EU military power.
The present challenge for deterring violent conflict on the European continent is thus not about the quantity of forces or the sizes of budgets. That's what superficial voices want us to believe, and it's also a myth that's conspicuously self-serving for the armed bureaucracies and arms industries in Europe.
The real challenge is to let these forces be relevant (and meanwhile, we could actually reduce military spending and force numbers and still stay safe). "Relevant" means "timely" and "suitably prepared". A suitable preparation is a preparation for defence; insurgents won't attack us, if any power dares to attack us it's going to field a powerful regular military that's used the time it had to counter our doctrines, our technologies and that's prepared to exploit our weak spots. Forces focused on how best to occupy some distant country and force a puppet regime on it are a waste of money and time in regard to defence.
"Timely" is about how quickly the suitably prepared forces arrive.
The most plausible scenario for an attack on our alliances (NATO and EU) isn't a full-out assault to make us all speak Russian, Chinese or Arabic. It would rather be a quick coup de main followed by a fait accompli, a "I'll use nukes if you try to take back what I conquered!" message. A very promising counter would be to make the original coup de main improbable by showing the ability to counter it with enough military power IN TIME.
The old NATO "strategy" of counter-concentration is bollocks, for it assumes that an aggression can be predicted in time and politicians actually act on the intelligence without prohibitive decisionmaking lags.
We need forces either where we'd need them or able to get there real quick.
This is how I'd rate the different timeliness of land and air power:
(1) high readiness forces in-theatre (incl. allied forward-deployed forces)
(2) air-deployable forces with resupply secured (including with prepositioned material)
(3) low readiness forces in-theatre (including personnel reserves)
(4) high readiness road march-deployable forces (incl. tanks on tank trailers)
(5) rail march-deployable forces (only diesel locomotives are relevant)
(6) low readiness deployable forces (including deployment by sealift)
The cut for actual relevance is in my opinion among those forces of category (3) that are close and those that are very far on the continent.
The typical air-deployable forces would be air power (self-deploying air force aviation with core ground crews deployed by transport or passenger aircraft) and "airborne" forces. The "airborne" forces might do a jump, but not close to known opposing forces. Such a jump would rather serve to deploy them farther forward than the most forward safe airfield. Surface-to-air missiles are still less long-ranged against slow* transport aircraft at very low altitude than the 500 km limit in ground-launched ballistic and cruise missiles of the INF treaty. So airborne forces may arrive a few hours earlier on the scene if they jump than if they land at some safe airfield (that's probably overcrowded anyway).
There are problems with both air power and airborne forces. Air power will likely not achieve much initially, for Western air power doctrines have grown to depend on either a slow force-build-up (1990) or even a long conflict (Vietnam, Libya) and enough time to first go after the opposing defences (air defences, fighters, supporting HQs) and then influence ground war. Western air forces are poorly suited to make themselves felt on the ground within hours or days even in face of powerful defences. We could change this by investing more into ground--launched cruise and ballistic missiles, but we've allowed our air forces to idolize fighter pilots so much that the ranks of air force generals are dominated by pilots. Pilots don't want a force of trailers with missiles ready-to-use, they want manned combat aircraft! Thus we neglected GLCMs and GLBMs.
Airborne forces have horrible problems as well:
- poor if any artillery power
- poor anti-tank power (dependent on shaped charge principle, especially anti-tank guided missiles)
- poor battlefield mobility (hardly any armoured vehicles)
Airborne forces that qualify as quick reaction forces for collective defence need to
(a) have these three problems solved (maybe with an arms room concept in which their artillery battalion switches between towed artillery and air-deployable self-propelled guns as needed)
(b) they cannot be used as stand-alone formations (they'd be reduced to infantry reinforcements for mechanised brigades)
(c) they can only be used for niche missions such as defending a bridge, towns/cities or woodland
A plausible recipe for collective security at spending levels that include hardly any avoidable waste would be focused on collective deterrence, not on the interests of warmongers, not on the interests of the armed bureaucracies, not driven by path dependent customary force structures and habits.
Europe is vastly more powerful than needed and is spending vastly more on military power than wise, regardless of the uninformed gut feelings of people who claim otherwise. Yet Europe's military power is not oriented at doing its noble core job; providing collective security through effective (and preferably highly efficient) deterrence.
I am under the impression that the reorientation towards this is half-hearted and slow, but most worryingly, it's low on ambition:
So-called quick reaction forces are small, patchwork and not really quick. The quickest-deployed forces are predictably ineffective in the relevant collective defence scenarios.
Maybe the collective defence activities are 100% satisfactory and effective despite being largely symbolic, or rackets to serve the armed bureaucracies and the careers of their political masters. Well, if this was the case then that would be a most convincing reason to still become more efficient, and to cut spending levels accordingly. What can be done by much at poor efficiency and rather symbolic effectiveness can surely be done at much less expenses if the efficiency was better.
*: Either fast or very low altitude, one cannot do both with transport aircraft..