Sorry to bring real life into a fantasy discussion but the pacing doesn't seem sudden or rushed to me. You hang out with someone for a while, you share some significant moments and you make a pass. I get why it might seem too modern if people are hoping for a medieval courtly romance but I found the pacing refreshing natural.
I kinda agree with you, the reason why I say that it feels sudden is because it all happens at the same time even with characters you haven't tried with.
Some people will make you work for it. Others won't be difficult right off the bat.
Seems perfectly natural to me. I can state with 100% confidence that some people "just give". It's nice when they don't worry and just make good things happen with you. Don't need someones life story to have good times. Information and awareness is only important in regards to safety and pushing past closed minds. If someone is distant with you, like Shadowheart, then they're a bit more "close minded" for example. You have to prove their irrational fears are unfounded.
Meanwhile, the vampire will sleep with just about anyone. Probably makes it easier to snack on them too. Just a nibble. Promise.
Wyll is like... impossible. Seriously, people have tried and tried and tried and can't figure him out. That might have been because his romance arc is unfinished though. Dunno if you can with him currently.
This means we have variety in all dynamics. Some people make it easy. Others need to open up. Others still are just plain stubborn (Wyll). Then you have to talk about how actions change feelings and stuff. Seriously, that's how it works. We don't have enough of those kind of conversations.