So, yeah. The Enclave didn't actually create vertibirds as a post-war thing, or their mk2 power armor in fact, as both show up as pre-war relics. Have there been many conversations on how to reconcile these issues, rather than seeing them as retcons?
I have a few ways I have sorted them out. For the power armor; it's the frame and power source that the Enclave mostly created. A superior and tougher frame, and a single power source that removes reliance on Energy Cores. As for the armor, they used the same visual design as the X, but used superior materials. That works for me as a simple one. I see the Commonwealth as simply having a wealth of inferior frames and models, and that the energy Core design is an outdated frame that has all but been phased out elsewhere. Maybe retcon that the T-45D in FO3 was also supposed to use them, but it was handled off-screen, because I can't see how to reconcile their use of the more primitive armor in 3 and the power requirements in 4. In short, I simply assume that all the armor we see prior to Fallout 4 (for the most part) are superior models, made in the last years/months of the war, and the inferior (power core requiring) ones have long been taken apart for parts.
The vertibirds are perhaps a little easier. The Enclave Vertibirds? There were too few to rely on in war, impossible to make in any number that make it worthwhile to waste materials and manpower, and tough enough they they are kept closer to home (the Citadel) for defensive purposes. These Vertibirds in Fallout 4 are actually what the West Coast Brotherhood came up with for their war with the NCR, using improvements from the plans taken from Navarro and compromised to be useful to a faction that has less resources; for the body/hull, they used the pre-war versions and designs. I can see the Brotherhood raiding old airbases, taking the old pre-war shells, and refurbishing them. Maybe even using pre-war factories (and materials from the Pitt?) to make new ones in small numbers.
in short; the Enclave armor kept the look of the pre-war cream of the crop armor, but it's still a new creation in all but aesthetics. The vertibirds the Brotherhood rely on are refurbished, albeit upgraded, pre-war models salvaged from airbases. The Enclave ones are too precious to throw away on operations.
It's all basically headcanon, but I hope reasonable. It's not like we were given a great deal to work with.
Has anyone else come up with anything? It's nice to have several explanations beyond 'lol, retcon!".