Yep. They are all great. Photon is my favourite so far. Sleek & Fast with a Black & White theme. But they are still a Work in Progress amd lack features. I tried them a week ago. I always end up reverting back to lemdro.id
lemdro.id is just a frontend, however it does have a special shortcut to the backend that allows it to function better under heavy load (on lemdro.id specifically)
They're not themes, but entirely different web apps for accessing the Lemmy frontend. The default Lemmy-UI is just one of them and could be replaced outright.
Those web apps are made with theming in mind? One thing that Old Reddit allows is subreddits having their own css theme, some of them are better than the default old reddit. Suppose I'm the owner of a Lemmy instance and want to replicate the look of a specific reddit community, would that be a pain in the ass to do? The same question for Photon and Voyager, as I imagine some instance might want to further theme it, by changing things more thant just the banner and icon.
Wouldn't it be better to write those interfaces as Lemmy-UI themes? Or is that impossible?