Sometimes imposing artificial limitations on a creative endeavour breeds innovation. Part of the whole point of Watchmen was to deconstruct the genre of superhero comics and that included intentionally breaking a lot of the old rules. Granted some of those rules were there for very good reasons, but that's what you find out when you experiment.
Also keep in mind that as the medium has evolved, certain practices come loaded with tonal connotations. One of those is the idea that thought bubbles are a bit on the cartoony/comic trip side. More appropriate to Garfield or younger skewed books than "Serious Dark and McGritty" style books. Corny, hokey, cliched, retro. Pick your preferred adjective.
Also keep in mind that as the medium has evolved, certain practices come loaded with tonal connotations. One of those is the idea that thought bubbles are a bit on the cartoony/comic trip side. More appropriate to Garfield or younger skewed books than "Serious Dark and McGritty" style books. Corny, hokey, cliched, retro. Pick your preferred adjective.