The two routes I know best are EAT-SEA and YLW-SEA. EAT-SEA has gone from 4x daily (or maybe 24-26x weekly) in the Q200 days (connections worked well to most destinations) to 2-3x daily in the Q400 days (connections worked to some destinations) 1x daily in the E175 days (connections only work to destinations with frequent service from SEA). For a 98 mile flight, give me frequency over comfort any day. YLW-SEA has gone from 2-3x daily, year-round to 5x weekly seasonal service (December-April only).

I love the E175 for making thin 500-1700 mile routes possible in great comfort, and in principle the A220 for anything it can fly (except the one time I was actually on an A220, to fly YLW-YUL, we sat on the plane at the gate for two hours before the flight was cancelled due to a non-functional lav, which didn't leave happy feelings). The QX Q400s were no fun when they were used for long routes like SEA-STS or especially long routes that could clearly support more comfortable planes like SEA-OAK. But the Q400 makes an entire class of missions economical, without which it's very difficult to efficiently use air travel from where I live. (And both Air Canada and WestJet configure their Q400s with more comfortable, better-padded seats than AS/QX did — but I still loved the QX Q400s.)

And a semantic point: E175s are not ERJs! I will definitely take a Q400 over an ERJ (the 35-50-seaters that I at least can't stand up in, although the single seat in the port side is kind of nice). Thankfully, AS has never sold ERJ flights under their brand.