A lot of people have wished the Headmaster gimmick was removed and I absolutely DO NOT get it. It's an EXTRA play feature. It's more toy and better IMO. Heck I'd rather Headmasters were added to every toy ever than taken away from a toy that already had it.
I wish that toy didn't light up, or have an accessory figure or a firing weapon is a weird idea to me. Headmaster partners are great and imo there's no negative to them. You get another character and toy for free.
-ZacWilljam, who cares if the character wasn't a HM in the 80s it's a good gimmick. Let everyone be headmasters ever. Why not.
If you really love Headmasters, I can see that point of view. But not everyone loves Headmasters. They fundamentally limit the sort of head shapes and sizes a bot can have, which is often one of their most uniquely defining traits, so it can be a huge turn-off aesthetically. And practically, it's a tiny figure that can easily be lost, leaving the larger bot headless... which is slightly less than ideal.
Setting those aside, it's also extra tooling, complexity, and assembly required for what would otherwise be a really simple part of the end product. All of that eats up budget, which otherwise could have been spent elsewhere on the figure.
So no, it's definitely not just more of everything good with no negatives. It's like anything else. It can be a net positive, negative, or neutral depending on the execution.