phpBB works, it dones’t work well.
Also, sorry, IMO this is flawed logic: “if phpBB was that bad it wouldn’t be the most popular forum platform out there”.
It’s the most popular because it was first and easy to set up and nobody really challenged it or cared to. Jeff Atwood, of Stack Overflow and Stack Exchange, also believes that forums like phpBB are broken. As well as the Vanilla Forums team.
Just because it’s popular, doesn’t make it better. SMF sucks too BTW. ;-)
At this point, if I changed it would be Discourse but I’d rather try to get Banter launched instead.