I didn't spend long testing everything -- I was in sandbox mode seeing how well a bunch of different mods played with each other -- so I may indeed be wrong. I'm basing it largely on a couple of observations:
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I just shelved a 800-hour Space Exploration run where I have 0.99 threat biters. There, a 3000 health Spidertron is a painfully expensive unlock requiring colonization of multiple planets, and scales decently well into the endgame. It's powerful enough to individually purge an entire region of biter nests, but is balanced well enough that it will quickly get destroyed if the player doesn't handle it with finesse. (Obsoleted by the endgame, by which point the engineer can personally outrun the Flash and has thousands of shield hitpoints, when he's feeling merciful enough to not just exterminate all life on a planet from orbit.)
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While testing these mods, I crashed a DeLorean into a trio of (minimum threat) nests, came to a dead stop and watched as a swarm of biters futilely hammered away for a painfully long time while I casually dislodged myself and drove away with more than half of my health remaining.
I agree the vehicles probably are balanced relative to each other and would probably work well in a PvP game. On the other hand, they look like they're a bit much for dealing with vanilla biters, and definitely outclass everything else that's available. The troublesome bit is the "everything else" are the mods that add interesting features to the core game like new mechanics, recipes, surfaces and secrets. But if you just want to keep them internally consistent rather than syncing with popular content, I can understand that.
I am aware of the cost adjustment slider, but an expensive unstoppable juggernaut is as unstoppable as a cheap unstoppable juggernaut. I'm going to be using AAI Programmable Vehicles this run to try out RTS tactics with multiple vehicles, so I'm thinking I'll probably want somewhat squishy troops to keep things interesting. The weaker vehicle mods will probably work better together, although I'm a bit bummed out since they don't have the level of detail you've put into your vehicles (bombers that drop bombs, unique horn sounds, specialized ammo, etc).