Please explain. Why meaningless? Isn't the timing off vehicle call-ins a very important point? Lets say for example Royal artillery commander would be of any use and people would choose it. While the Valentine isn't very early in 1vs1 already it hits the field in a 4vs4 when it is absolutely redundant because there are multiple medium tanks on the field (+shreks +pak..).
Binding it to a Tier level (even if it is a side upgrade) would be the only way to have the timing the same across all game modes.
It would be meta flip, but would not change much as a whole. Honestly, only call in i see as crucial is croc and calliope because of their crazy shock value. With soviets you usually spam maxims, which means t2, which means at, and also mines, all of this plus some teammates help would be enought to get kats (there is no reason not to), and get cp from kats. Your IS2 and t34-85 may or may not be delayed depending on fuel control, but they are not so cruclial to count them as a game changing factor. It is more of a compliment for already strong lategame than lategame deciding factor itself.
Royal arty problem is units cost-efficiency, even if they were 3cp, they dont look so amazing.
Plus units are wastly different, just look at light tanks: p2 is good infantry killer with lots of hp, comes faster, but cannot fight other light tanks; t70 is good overall, have recon to spot for itself, but dies to 2atg shots (3 if you can pop repair inbetween), thus more risky to use; than stuart which is good against vehicles, bad against inf, have lots of hp and can repair itself.
Same goes for heavy call-ins. is2 and tiger1 being 13cp doesnt mean they come at same time, soviets probably would have is2 faster since they play more agressively, while wehr is more of a defensive faction. Plus, again, different performanse, different roles. Is2 basically is a damage sponge with ocasional RNG wipes, while tiger is fastfiring tank, which you want to use on med-long ranges.