I think it is intended so that you keep and preserve units you recruit for a long, long time and think before disbanding them. The player attachment and immersion is a good thing.
...At least that looks like the concept. Not sure how it will work out in the game actually.
EU4 has drilling that evaporates away so fast it becomes pointless after a while unless you want to play with space marines.
Victoria 2 had two things at once - "general prestige" and "brigade experience", intended to make you keep and use experienced units and commanders from start of the game to finish, but those two were gained so slowly that it was pointless.
Can't say about HoI4, but I think unit experience gain rate is decent enough. Divisions that have been used for fighting from 1936 to 1945 would be the "elite" veterans, while those raised around 1940 would be very experienced but still not the same level, and new recruits would only go up to the standard boot-camp training levels. And replacements for any battle casualties/attrition reduced experience as well I think.
My biggest worry at this moment is whether we'll be able to rename cohorts and ships ourselves properly. EU-Rome didn't have that feature because they forgot to put it in, Vicky2 didn't have this feature because they forgot to implement it again (alongside rest of the entire military system really), and Stellaris didn't have a renaming feature for armies until recently.
Other than that, the game looks great.