On the topic, why is it that each Tier is locked behind its counterpart instead of being able to upgrade to next tier like: "battery powered miner to battery powered miner mk2" and so on? seems a bit odd.

I could perhaps make a recipe for a conversion back to the regular vehicle? That would mean to upgrade a battery-powered-vehicle-mk1, you would turn it back into vehicle-mk1, upgrade it to vehicle-mk2, then convert it into a battery-powered-vehicle-mk2.

It's not the ideal solution, but doing it the Right Way would require that I parse and understand the upgrade path of the original mod, and I don't know if I can do that reliably.