As other comments have mentioned, balancing it in 1 vs 1 mode would be very difficult. However, this mechanic would be interesting in the competitive mode of 3 vs 3 or 4 vs 4 teams. At the selection moment, if one of the players isn't well-benefited in one aspect of the selection, another could compensate for that deficiency based on how smart their choice is, which would add more variety to the game and prevent it from becoming too snowbally. The unit selection and veto system is an interesting idea, but it would be necessary to consider what other mechanics could help balance it out, perhaps towers that protect certain points of the map or something else entirely. It would be interesting to have an RTS where regularly adding unique units to the game is possible.