Yes it is except when it isn’t. Maybe there’s a reason practically no Adwaita theme alternatives ship with Debian. Maybe not. But, using Gnome, it’s the default theme or nothing. I have to admit I don’t know from themes. However, there are lots of Gnome themes available from theme peddlers.
Recently I became fed to the teeth with claws-mail, which is a GTK app. In Adwaita the foreground font color is too dark (gray) on top of the background highlight (blue). My eyesight had deteriorated to the point that I just couldn’t read the Subject of the current eMail, so I shopped for a new theme that would be … adequate. I didn’t have time to try them all.
I settled on Ant by EliverLara. In this theme foreground font color (white) on background highlight (salmon) is just barely visible. I use it only for claws-mail: