The parts in game for new vehicles are very unfriendly to players and a blatant sacrifise of player experience for gaijin revenue. Every new tt and sqaudron vehicle that is qresearched requires a considerable amount of time to spade, which means that during that period of time, the vehicle is underpowered and not competitive. take, for example that challenger mk3, stock, it has a L23A1 shell, identical to the one on the mk2, but, the mk2 is 0.3 br lower than it and a stock mk3 does not have access to thermals and is also more sluggish, still, a stock mk3 is rated higher in br, so this results in it being much, much less potent and the grind for parts is more painful.
In addition to this, the L26 shell, which make the mk3 worth its 10.3 br, is at the 4th tier, meaning that players will have to take a long long time using the underpowered L23A1.
Grinding modifications are not only damaging to user experience, they are also not very realistic, no chally have been built without the thermals, the lrf and the apfsds that we have to grind for, no abrams have been forced to use heat in combat, and no leo had to invent its dm23, 33, 43 or 53 again as an extra addition to it when it is produced.
Also, having to grind modifications is another form of copy-paste, Players eventually get sick of having to grind out the same shells, parts, thermals and engine upgrades on one tank after another. Grinding for the same shell across multipule similar vehicles, like the dm53 on leoa5, 6 and 7, on the PSO, Pl etc are very much redundant and time wasting. Exspecially with mbts that had to use heat as a stock shell, tell me, How exactly r u supposed to fight an era covered t-80 in an abrams without lrf, apfsds or thermals? This just discourages players as it kills off all the excitement of getting a new vehicle and discovering that is is no different from an old one but for the higher br and the better enemies. (I was looking forward to the chally mk3, but the grind for l26 is a bit too painful for me)
Lastly, people who are grinding modifications tend to one death leave, ruining the experience of their teammates. I personally am guilty of this, as I am trying to get the vehicle to work well as quick as possible. I have also seen several of my friends do this in game and it seemed to be a widespread practice.
In the end, the modifications might mean a bit of revenue for gaijin, but is is a huge sacrifise of player experience and I do not think it is worth it, even for Gaijin.