For stuff like that I'd like something akin to the Energon Omega Supreme "solution", which is a sort of mini-head for the Cybertronian bulk to have. Would look silly though.
That's the trouble with the mental linking, is that some functionality almost has to be reduced on the part of the 'advanced alien robot' Cybertronian in order for the Nebulan/human/whatever partner to play a role. This includes self-driving and auto-aim (or even aim-assist).
Powermasters basically being Mini-Cons, providing a plug-in power focus and/or power boost, I can get with. Basically a battery/power bank, or even an adaptor -- could be acting as conversion engines, helping process an otherwise unusable power source in ways a native Cybertronian system can't.
Headmasters make sense if you're willing to shrug off the inherent "self-driving" nature of said advanced alien robots. Maybe the characters are younger and not yet able to intuitively nagivate effectively in altmode? But again, that's reducing functionality and autonomy. I do like the character dynamic of them having a copilot literally in their head, though, and there's fun story possibilities there that I kinda prefer to the otherwise-better Transtector solution.
Targetmasters IDK. Maybe if there were a mounted weapons system in altmode that they controlled (but see Headmasters, same problem). Or I guess the point of them could BE to arm an otherwise unarmed altmode. Again, like the Headmasters, there are possible story reasons that can be worked in to justify this -- the altmode disguise precludes weaponry, they're pacifists who avoided weapons initially, etc. But them controlling the firing arm in robot mode I'm not a fan of, as again that takes from one just to give the other a reason to be around. It would be interesting for a character like Misfire, who needs someone to take the wheel firing arm and of course hilarity ensues with Aimless, but that's... one pair out of several.