I actually haven't played Royal, (you'll see that in my Royal post) but I watched a Let's Play online for it and skipped some parts... Because of how long is it, I don't think it's worth playing the game again. But the new antagonist is so amazing.
For you, I recommend you play it if you feel you want to.
Devil Survivor is really good. I was surprised when I saw it was developed by a different team than the main SMT series. (The team didn't work on any SMT game before.) Because it the SMT identity in it is perfect!
Didn't play Record Breaker though, I only have some familiarity with Devil Survivor 2.
I do have a habit of replaying my favorite games sometimes, if Atlus don't release a new Persona game that's as good as 5, I may end up replaying it eventually.
Oh I didn't know about that! It makes sense, Devil Survivor is a successful game but they're not making any sequels/spin-offs for it, if it was made by the original team they would've milked it 😕
Record Breaker has an added post-game story arch, which I haven't played yet even though I finished the game twice, but I heard it has enough content that you actually start over from lv.1 and go all the way to lv.50.