Going to post because my site fits most of what you want and frankly power systems sites are not popular at all in animanga right now -- I'd go as far as to say I'm one of the few advocates for it left here. The only other ones I'm even aware of are in the Fire Emblem sphere, which you've specifically excluded in original post.

We're in transition phase after a timeskip and a site plot reorientation, but the good news is that at this point we're basically RWBY inspired rather than RWBY AU so you don't actually need to know the source material at all. The lore is present but mostly done IC and frankly the only thing you need to know is that we're doing a standard Government vs. Rebellion plot and those are our factions.

We have a progression system that's been going steady for two years OOC set up with exponential gains between ranks so the amount to catch up to someone's rank past a certain point is noticeably less than it is for the higher person's rank to increase in a skill. We have combat systems largely used for PvP and a streamlined system meant for group threads/events that is specifically designed to remove stalling and encourage proactive play.

We're recovering from an activity downswing right now, but even then we have multiple posts a day with events in the pipeline which always result in a decent activity spike. I've completely moved on from having a plan for the site plot overall, and have shifted basically entirely to letting players decide what they want to do and how they want to change the setting and refocused my energy on my own faction. Overview blurb below:

The Remnant Project is set twenty-eight years after the Great War in an AU timeline and is focused primarily on the struggle between Council forces and the so-called "Revolutionary League" in a brewing civil war. The site has a progression system that is designed to last through years of user play, and will attempt to deliver on the fantasy of starting off weak and progressing into a legitimate hero with a list of significant accomplishments worthy of someone with that title by way of giving people clear ways to enact change in the world and site events that will change the setting in both big and small ways over time.

Thank you for the recommendation, I’ll give it a look over (I’ll admit I don’t know much about RWBY’s base story though lol). To anyone else just in case I’ll also take the time to emphasise that power system/stat-based isn’t the only thing I’m looking for, I’m fine with almost any type so long as it fits the other points, including narrative RPs without combat at all. 

I thought I had replied to this one...

Hi! We at Remnants of Fate would love to have you come look around! We are an original animanga rp site that as much as I try to put the plot into words I really can't without rambling because there are multiple plotlines and factions and species and really it's best if people just check us out and ask questions.

What I can say though, is that we are fairly active as a community, moreso on the weekends. We are mostly adults with work and school and understand when life gets too busy, but we all reply pretty often. We live in discord too so that's always good. Everyone is very welcoming and friendly as a community, and we all love plotlines. We've been open for about 2 years now, so there's no real worry of it disappearing within a few months, but that being said, while the lore is pretty built up and established, it is really easy to come in and do standalone things. The plot often will find you, and the admins are very open with answering all questions you might have, so knowledge of the lore is not exactly necessary in most cases as long as you read the bits of information in the main board to understand the setting then you're golden. I know you mentioned lore based sites are pretty hit-or-miss, but we're pretty open about it so it's pretty easy to find yourself wrapped up in it. We don't have a stat system exactly. Our upgrades go based on points and participation in site events, and admins tend to give out points like free candy every so often.

So please feel free to come check us out, stay and hang out to chat and get to know the community before joining, or just wander on through. We look forward to seeing you and good luck with your site searching!