And you still wouldn't. Flamethrower Engineers aren't dominating games now, and allowing them to upgrade to retain some relevance in the late game isn't going to change that. Its just a way to make them slightly more useful when forced into combat, which is the entire point of this thread.
They are not supposed to be useful when forced into combat, you can tell that by looking at their price and their stats. That's the point I'm making.
Thats funny given that the Minesweeper upgrade is clearly the no brainer option right now. So tell me, should we split the repair speed buff into its own upgrade to force choices?
Its very much not a no brainer. You are trading 25% your firepower to repair faster. If it was an absolute no brainer you wouldn't be trying to make both available. You are either getting the upgrade that makes them better on the front or the one that makes them better off the front. Decisions need to be made and that's a good thing.