When the latest expansion was released, it came with 2 dungeons plus a third retuning of an old-world (vanilla) dungeon. Both Storm Legion and Nightmare Tide had many more dungeons. Also, the dungeons are undertuned, so got "easy" quickly. I recall folks getting the Conqueror achievements in SL and NT after a year, and now they're being gotten after a month.
Trion also didn't release a raid with the expansion, and it's still not out. Even the group content that did exist was sometimes offline to fix it or kill exploits. It just feels like an unfinished and half-baked expansion. A lot of people are biding time hoping the raid is good enough to be engaging.
Right now, it's hard to say really how active the chapter is. I think we have maybe 5 people on in ET evenings, but this week with the holidays is a mixed bag. There are folks who stay on till 1am ET. We're a relatively small guild, though, with perhaps a dozen active members. You're not going to find 10 people on at once very often.
You're welcome to come join us, if you think we're a good fit for you.
The power-leveling trick in CC was removed when SFP was released, so that option is gone. If you want to level up, you'll have to do it through leveling up. It could be that there are folks, especially in the current drought of content, who are leveling up alts, and you'll be able to group with guildies. Speaking only for myself, all my active toons finished NT at level 65, so I'm not going to be exploring NT content for a 6th time. Which really gets to the crux of the matter: What's new to you is, for folks who played the last expansion, stuff they've been in for two years. We had a couple of members join in the Fall who took NT off, but they did the leveling burst to get to 65 before the expansion. I don't know how much population you're going to see leveling up. Best to ask Fires, who is leveling through NT these days.
It may be that you'll find folks to group with, or it may be that you'll end up doing it alone. It could be that if you need help on a fight, someone will be able to swing by and do that. But most of the Rift Chapter is level 70 now, so aside from alts, you're probably not going to find many folks leveling through the NT content. As I said, though, I've not had reason to look. It could be that NT zones are populated.
Mumble can be active. There's social interaction there, even if you're out in the world on your own. But that may not be what you're looking for. Personally, I end up soloing every game, every expansion, because it's hard for me to dedicate X hours to sitting in the chair, and I need to be able to get up and do stuff on short notice. That's not really conducive to groups. You need to do what you enjoy as a way to spend your time. In some respects, all these games are tedious, without the group aspect, and without beating the challenges that require a group, and can't be done alone. I think that's why raiding is so important (and why the lack of it right now is putting Rift into the doldrums).
We have good people in the chapter. If anyone asks for help, they get help. But let's be clear here, if everyone who is online and level 70 and you're level 60, you're not going to get folks to come run NT content with you. If you've done a quest chain and need someone to help with close a rift or do an end boss, you'll likely get that. Maybe you'll make a friend and inspire someone to run an alt with you. But the social aspect here is like it is anywhere else, something with give and take and mutual benefit.
MMOs are really just social clubs: Like any other social club, folks with shared interests get together to explore those shared interests together.
But right now you are behind the curve. You can make the effort to catch up to SFP, and then find people to group with in the new content. Maybe you'll find folks to group with on the way from 60 to 65. I don't know. But I think you need to look to yourself. Phrases like "imposition on them" and "knows what they're getting into" sound like you're looking for a guild to cater to you. That's not how it works, at least not here. We'll welcome you, and support you, and work with you to be the best you you can be, but at the end of the day, you need to stand up yourself and find your own enjoyment.
If this says to you that you don't want to come join us, I understand. We're not going to ask you to join our ranks. Joining is your choice.
You are welcome to join this group of fine people, if you want to, and see if perhaps it works out for you.