TMLs are a bit similar to nukes in that they are basically always a decent investment in team games on semi open maps. You only need one player to make them, but every base needs defenses and if even one doesn't make those, you get a huge return on your investment.
As a result they, like many similar aggressive tools, are very strong in the rating range where people are good enough to use them, but not consistent enough to always defend against them correctly. You could argue that they are straight up OP in the 1k-1.5k rating range.
Sadly this imbalance of units in different rating ranges is pretty much an unavoidable side-effect of the huge game complexity. Subs and stealth units for example are just completely broken in the <1k range as nobody there is able to deal with them correctly.
Maybe there is a way to balance TMLs for more rating ranges while keeping it interesting. Maybe TMLs not killing mex wrecks is a way to do so, but honestly I'm not convinced they need to be changed at all.