I'm not aware of how good the clients worked at the time, but I believe there still are some features that were developped in the meantime that were not there:

- privacy in general, with asynchronous e2ee with forward secrecy and minimization of metadata

- reactions. They might sound childish but they're a good way of acknowledging something without polluting the chat itself

- proper support of files, including easy display of all media and search

- probably the biggest: voice/video calls. "Some support" clearly wasn't good enough.

Now it's a really hard place for Pidgin to sit in, because it can only follow what the protocols do, not push them to do more or to standardize.