Agreed.
The idea of DC's 'trinity' was based on the idea of Superman, Batman and Wonder Woman were the only three characters who saw continuing print during the Golden Age. Comics drifted away from Superheroes after the war and Romance, Western and Noir took over... but those three were still popular enough that they survived the purge.
That was a LONG time ago. Wonder Woman has been canceled a few times now... Especially around the Infinite Crisis time if I recall. She's had more reboots than anyone else I can think of that COMPLETELY upend her origin, abilities and mentality... and she's never really popular outside of 'the first woman hero'. People like the general idea of her a lot more than her actual stories. She really flounders and has the weakest fan base... lot more than any member of a 'trinity' should.
So yeah.... Batman and Superman are DC's most popular characters... and Wonder WOman is who they WISH was popular.... but gets her slot more out of tradition than anyone else.