Really, what you propose sounds like an AWESOME game for good friends to have a blast, just as having a beers and pretzels tabletop game testing out the most OTT special units from the weirdest expansions for fun and giggles.It doesn't sound like a game that has any chance to become a competitive gamers favourite, or is even very fun to play for strangers over the internet.
Entirely possible. I'm operating under the advice of a game designer who said something like (massive paraphrase warning) "Don't try to design an esport. Add hooks to make it easier for your game to be adopted as one, sure, but trying to design one from the outset will get you a soulless, joyless 'game'" With how this game is taking shape in my head and in a handful of limited prototypes, any competitive scene that could possibly grow up around it would look very different to, say, Starcraft's. My use of the phrase "competitive RTS" was really just redundant - I meant the stereotypical RTS, where two or more players go up against each other.
This is also my opinion. I see many games that are E-Sports favorites because of its balance as quite soulless. Not boring to play as long as you are into ultracompetitiveness and can get satisfaction out of that, but certainly lacking in flavour. And from playing games that have inherent troubles with balance I can say that this is not as much of a problem as some whiners make it sound like, as long as there are always multiple viable strategies, it doesn't matter much if one is a little bit better and one is not as good.
With that said, I would concentrate on balancing not so much the "fairness" of your design, but its "rage factor". Giving players the ability to "officially troll" their opponents can be fun in some games, as long as its tightly controlled. The last thing you want is that your players feel their opponents using cheap tricks, "cheating", and doing so by using (or "abusing") the games own official rules. Its when a not so balanced game turns into a broken one... and even if this would balance out over many games, many players will just look at that one match that made them angry like hell, forgetting the other matches where they owned....
That is why I have my doubts about too much interference with the opponents resources pre game or the veto system. I am not 100% sure I understand how you want to implement a veto system in a competitive game, but looking at the US politics, we see how a "veto" gets seen when the two parties involved are so hostile to each other... neither side sees anything good about it, not even the party that was able to veto their "opponent"...
As long as strangers are playing against each other, I would be concerned about making sure everyone gets to have some fun. Now, I know this is a hot topic about games which try to make sure skillfull players don't own too much, but given that as a dev you should be concerned about more than just single players, it does make sense to try to bridge the skill gap a little bit. So if your pre game is too much about skill (or knowledge), that gap will widen even more.
Making the pre game too much about luck would on the other hand leave players with the feeling that they lost because of the RNG... which can be good, to some extent, very few players want to face the truth that they are not the top 1% of players and rather blame it on the RNG.
But if the RNG starts to troll them before the game even begins, that might be too much for many.
Now, there is another thing. One of the interesting parts about wargames and strategy titles is to have to adapt to your surroundings. Its what makes or breaks a real militarys strategy. The combatant who is better able to adapt to their surroundings usually wins. Bringing tanks without infantry support into a city is usually ending badly. Letting infantry attack a machine gun nest over no mans land too.
Now, I did write before about why forcing the player to re-adjust every game could be too much... but you are trying to turn this thing on its head. Instead of the player having to adapt to the environment, they can now adapt the environment to them. That is not how war usually works. Which is fine if you want to go more abstract.
From a realistic perspective, a "random" procedural approach would certainly be better. How well that approach will work for an RTS or any strategic game IDK though....
The players involvment in pre game "environment setup" should be quite limited. You usually don't have the ability to bring in the big tools to move cubic kilometres of earth before a "random encounter" somewhere along the frontline.
I do see this as a good tool to make a onesided "defense" game mode more interesting though. Give the defender the chance to setup their defensive structures before the game starts, and also to change the battlefield within limits. Give the Attacker the ability to plan their attack waves at the same time to keep the attacker busy while the defender sets up his fortress and death zones.
Then give the attacker a limited ability to scout the defenders defenses pre game so its not just a mindless slaughter favoring the defender. And the defender is forced to adapt the well prepared strategy, and maybe even make sure their initial setup allows for multiple viable defense strategies should their opponent successfully avoid one of the traps they set up.
That would work without any veto system, as the whole game made is inherently assymmetric. Hard to balance? Yes. But could be very interesting, and makes exensive pre game environment changes quite realistic.
Other game types could have different pre-game options. A "random encounter" could have a real randomly generated environment. You could limit the terrain generation so no side is getting too much of an advantage. You could place resources at fixed positions, if there even are any (a game made WITHOUT resources in a game that usually has some in every map could make for quite a different game... having to preserve resources yet still defeat the enemy would force players to adapt their strategies for sure)... like the only resources on the map are in the middle, an abandoned supply base each of the opponents are trying to get.
Maybe there is a "trench line" style of game mode, where both players set up defensive lines in their half of the map? They can go crazy on it, with no involvment of their opponent.
The only thing here is that there needs to be some "stalemate breaker" units that prevent a WW1-style multiyear stalemate, without making the trenches completly irrelevant.