I just think being one type and needing Energy of another makes them all worse. Some not as much as others like Charizard but still I think it's detrimental. You have to run cards that don't fit your deck just to get the most out of these cards. Garchomp will be played with Fighting cards but you either have to run Irida just for Garchomp or not make use of it altogether. Just seems to me that if they made these Pokémon use the energy of the new type they would be better. If Garchomp used water energy and its attack attached Water Energy would it not be better?
That’s going to be contextual by type and availability of support. It’s not all downgrades, and you have to analyze what the Pokémon do, what they can deal with, what they are supported by, and what they can support.
Garchomp simply requiring water energy and supporting water pokemon to fix problems is more an issue with Fighting type having terrible overall support in general. Heck, this also makes Garchomp less useful due to available water type support existing already.
If Garchomp were its proper type, Fighting, then Garchomp would be in a worse spot than Garchomp being Water and requiring fighting energy. As a fighting Pokémon, Garchomp would no longer be searched by Irida, and its only benefit would be 1-shotting Arceus.
If Garchomp was water type and required water energy, well now it is a slower Palkia VStar that has a fighting Pokémon basic.
There’s gonna be no right answer to this and while some of these Tera Pokémon are clearly worse from their type change like Mewtwo and Vespiquen, Garchomp isn’t a straight downgrade.
Charizard losing Magma Basin is negligible as heck when it just attaches its own energy, and there is no benefit offensively or defensively from being Fire compared to being Dark right now, nor any extra searchability.
Charizard requiring dark energy just would mean it is compatible with Dark Patch, but it doesn’t care about that either. What is affected is the toolbox that can be run.