Heya, hardcore RS3 lover here to give some insight.
I was in the same boat as you when EOC came out. I quit and solely played Private Servers because I was really put off by the whole ability thing. After a couple years, I met someone who convinced me to try RS3. He gave it high praise and I voiced really not wanting to play because of abilities. Not the abilities themselves but because of it being difficult for me to use my hands to press them (I'm disabled and pressing a lot of keys is very hard for me.) However, he said I could use something called Revolution for it where the game uses your abilities for me when they're off cooldown. So I was like... fuck it. I'll give it a try. And I'll say, I haven't regret it since then.
In about six months, I learned so much about the game because of EOC that I didn't know before. I learned a lot about what it was to really want to learn something, how to put dedication and time into it, and so much more. The abilities are great and the overall PvM aspect of RS3 is, in my opinion, way better than OSRS. With OSRS, you go to TOB and Raids and that's it for PvM for the big bucks, honestly. RS3? You've got Solak. Telos. Nex: AoD. Raksha now. Hell, even the Elite Dungeons are absolute money makers. The caveat with them is putting in time and money into learning them.
If you put time and effort into learning RS3, it's so fun. I ended up taking quite a break because I was VERY close to max and Archeology was coming out and that demotivated me hard. But since I came back, I've pushed max harder and Archeology hasn't stopped me at all. When it comes to OSRS vs RS3, I feel like RS3 is so much better. There's a lot more to AFK for experience so you're not forced to look at your screen every second you're playing to get experience. There's a few like that in Old School, but not like RS3. Some say that's a downside of RS3 but I like it personally. Gives me time to do other stuff while also being able to train and work on my goals.
One of the things that IS a downfall of RS3 is that they don't really... know how to balance combat effectively? I'm not sure how to word it. What I mean is that at one point, Melee could be the strongest style, then they release one thing for another style and then that style is now top-tier. For example, Range was the worst combat style for the longest time. When Raksha came out the end of last year, a new Ability upgrade got released called Greater Ricochet. This changed the meta and has made Ranged the best style in almost every scenario (unless you've got bank to drop on melee I think?) I'm no expert so do take that with a grain of salt. Of course, every style is useful at different places, but the biggest gripe a lot of my friends have is that JaGex can't balance their combat and stuff like that at all without making one of them completely busted.
For how hard it is to get into it, I'd say it's a learning curve, but it's not horrible. As long as you can read, you'll be okay. You can fully customize your keybinds to your liking. You can play revolution (which I do) so you don't get overwhelmed then try Full-Auto ability casting whenever you feel comfortable doing so. There is no client like RuneLite or anything, though there's a plugin called Alt1 Toolkit which offers some little things like a clue helper. Nothing major like RuneLite can.
Sorry for the long post, but yeah. Wanted to put a bit into it so you have a general feel to it. If you REALLY want to learn the game, Ironman is the way to go since you'll be relying on yourself.
TL;DR - give it a try! You might really enjoy it!
