Also, of note, I thought it was interesting/unexpected the controller asked you to switch the 7700 for the reasons @Jim123 mentioned.
Something that I noted with a large percentage of students (and even some fleet-experienced pilots) was briefing to switch to Guard and 7700 if we had an emergency, especially on instrument flights. I would always brief that it would depend on if we were talking to anyone and with studs, sometimes need to get into a discussion about exactly what Jim was talking about and also how when you switch to Guard, you've just gone lost comms. For newer pilots, it's no doubt just regurgitating "the script" without thinking it through.
For ADS-B, I think it's really hit and miss on who is using it and when, in part because of coverage, and also just whatever system a particular controller may be using. Center seems to be a lot less interested in it, as I've been asked aircraft type multiple times. If they're radar coverage is good, then that may be the primary data.
When I was flying out to AZ last month, as I was going by White Sands, we were all getting jammed majorly. Center was very helpful and just asked everyone who reported the problem if they needed steering. At one point one of the airliners called and reported that his ADS-B was down as well (makes sense with being jammed). Center replied with, "Ah, okay. Um, how does that...honestly I'm not really sure how that works. Do you need it right now?" The airliner came back and explained that it was actually for ATC and just wanted to report the issue. Center replied his radar coverage was good and that's what he was controlling with.