I do find it quite difficult to melt bots without first destroying them due to core damage, though.
Yeah this is just a side effect of the fact that thermal weapons still do plenty of damage (unlike EM/corrupting weapons, which are much less likely to kill on their own). And the thing about high heat is even
before a target melts, they're already suffering serious consequences, sometimes deadly ones, so it's not always about the final meltdown!
If melting were as easy as corruption, thermal would clearly be the best weapon type, but each primary damage type is balanced differently for many different factors, so heat transfer and corruption are not completely analogous.