Hey everyone, I also attended AnimagiC.
First, I don't think that ring your bell and Lighthouse are all that similar, unless you're purely referring to the generally bright vibe both songs give off. Calling them "the same song" would also mean that about half of almost any random artist's discography I can think of would literally be "the same song" as well. It's called a musical identity, or simply an artist's style, if you ask me. It really just depends on whether you're into that particular style or not, I believe.
Either way, here's what I can tell you after hearing it once, albeit with less-than-ideal stage sound: yes, the song is very bright and certainly fits in well tonally and tempo-wise with songs like Mirai or Misterioso althoug it's certainly not as key-change spammy as Misterioso. I wouldn't really compare it to Lighthouse at all in terms of dynamics. The song itself is quite consistent, meaning there aren't any abrupt intensity or tempo changes. It flows very naturally and organically. It also follows a classic verse–chorus–verse–chorus–bridge–chorus structure, although the second verse was noticeably shorter than the first, if I remember correctly. The bridge is what reminded me of Kalafina the most, with its choral elements and key changes. There are definitely similarities to Mirai and ring your bell when it comes to the bridge.
In short, if you're into these brighter types of songs, I think you'll have something to look forward to. I personally enjoyed the song quite a bit, but I definitely need to hear it again with acceptable sound quality.
I like the other versions of RYB (in the silence, strings version), but the original has always been too fast for me.
I share the exact same gripe like you, but thankfully kanata isn't quite as fast, or at least didn't come across to me as overly fast.
