Purchasable vet is too big of a gameplay mechanic to be included in a single commander IMO. If it isn't part of the faction's core mechanic it shouldn't be included full stop.
I'm at a loss to figure out what the design briefs are that Relic are working to with these commanders. I mean, before this patch I thought that units vetted up too quickly (arguably they did) but the new vet system came in and it seems to be addressing that problem quite well... but what existing problem in the meta required this commander to be created is beyond me? if the answer to that is there wasn't one and they just created it for something new then im afraid that's bad design. Very bad design...
Research informs ideas --> Ideas inform deliverables
these commanders should be a way of addressing problems in the meta, not doubling it in size every month with new gameplay mechanics. I'm worried it's going too far now.
I don't really see a problem with commanders expanding the meta-game, in fact I welcome it. I also don't really see a problem with having the option to buy vet, especially with the new system.
1) The new vet system makes it so that higher levels of vet on units, while still stronger than lower levels, is not as extreme as before the patch.
2) Buying vet is a temporary benefit, with a permanent cost. You will never get that 20 fuel back, and as soon as the enemy units gain levels of vet your advantage is lessened.
3) Higher vet units are worth more experience. This is another reason I tend not to purchase Vet on Grenadiers. Fighting vet 3 grenadiers, or any other unit for that matter, will result in the Soviet player's squads/units getting experience extremely quickly. Further evening the scales.
4) All commander abilities are choices - basically, by picking a commander with the option to purchase vet you're giving up another option such as a doctrinal specific call-in or off-map support. Notice that the Elite Troops doctrine actually has ZERO in the way of off-map support. Not even light artillery barrages to help soften up entrenched ZiS/Maxims. This can be a huge drawback as the game drags on and other players can lay down strafing runs, incendiary barrages on your PaKs, etc.
5) Costing fuel (arguably the most precious resource in the game) it ensures that the player has to make a choice. Do I vet up this unit and gain an advantage RIGHT NOW, or do I save this fuel to get out my higher tech units more quickly? 20 fuel doesn't sound like much until you consider that using it 4-5 times over the course of a game means one less tank to bring in. This choice, as the metagame evolves around these new commanders, will separate good players from bad players which is ultimately a benefit.
6) There are still reliable counters to early game vet 3 units. People will have to adjust, simple as that. You can't expect conscripts to keep up with a vet 3 gren squad but you have Oorah to soft retreat and harass the map, you can throw molotovs which will gain you vet very quickly, and have equal effect on the vet 3 squad. Flame Engis will do the same damage, garrisoning houses will still be a great option, mortars, snipers, t-70s to chase retreating squads - it is entirely possible to play around an early vet 3 unit (and know that they've delayed their tech to buy that vet 3) - people just need to get used to it.