Firstly, this will have to be from memory of my old (actually current stable version) install of Pleroma, and things I have reacted positively on:

• There are back-end changes. Not sure what impact they have had, but I’ve seen the Pleroma devs migrating in things to Pleroma from Akkoma, so obviously some things have been solved by Akkoma.
• Regular updates - not something Pleroma can be accused of. Akkoma does a new release the second Saturday each month, and has a clear roadmap everyone can see (good expectation management).
• Admin options in admin-fe has been cleared up, and actually work. Still areas that could do with improvements (as they are inherited from Pleroma), but I remember settings that were confusing and/or plainly didn’t work for me in Pleroma “just works” in Akkoma. Possibly related to first point in this list.
• The rest is GUI things (and now I am only talking about pleroma-fe). I don’t know how, or who, configured the instances you’ve been looking at, but I have not encountered any other micro-blogging service, on the Fediverse or elsewhere, with as much functionality before (I have accounts on “everything”, for testing).
• Tree-view of threads (an optional account setting)
• A “floating” bar saying “Collapse” that always stay within reach if you’ve “folded out” a thread which turned out to be 3 miles long and you’re not looking forward to scrolling the next 5 minutes.
• Search (full-text) works fine (IMHO). Was a hit-and-miss in my old Pleroma instance, and could previously generate different results on repeated searches. With Akkoma it seems to “just work”.
• Lists and list management - massive improvement. Could still be improved further, but a huge step up from Pleroma.
• Follow hashtags
• Translations (I use DeepL)

A lot of the rest it has inherited from Pleroma, which was good to start with. Pretty much everything can be styled (except easily changing fonts unless you wish to code) from GUI settings (I run a Dracula inspired self-styled theme). It has Misskey emojis/animations, but I don’t care (at all) about those. Quote posting is the same as in Pleroma. It has all the filter-options from Pleroma too. There is nothing in Pleroma that isn’t in Akkoma. There’s lots in Akkoma that isn’t in Pleroma.

Most importantly, compared to Mastodon and pretty much all other fediverse micro-blogging services: it dynamically shows the contents in all threads, and on profiles. If it doesn’t have the stuff you are looking at (say, a profile), it runs off to get it for you, and within a couple of seconds it has populated that profile, instead of staying empty (like on Mastodon, Misskey, Calckey etc). The same goes for threads: it goes out to collect replies from people even if you haven’t seen them (or, their instances) before, instead of staying empty/invisible (like on Mastodon/Calckey). So…“proper” Federation.

But yeah, something like that. :)