Spoon is an awesome band that mostly flies just below the radar while still quietly releasing awesome records. They have been active since the 90s and they don’t have a single bad album.
The aptly named “The Band”. They are legends in their own right but I feel they are still underestimated in regard to the catalog and their influence. Big Star would be a close second.
The Smokey Brights. They have consistently good bangers throughout the years. Some of their music was featured in the indie computer game Pacific Drive, and it was fantastic. Save Us Sarah, Fancy Ketchup, and Ocean Shores are some of my favorites. Sad Boy Song #39 too.
My kids taught me to look at subscriber counts on a streaming service to measure popularity, I go to a lot of live shows and kept getting surprised at which bands were popular or unknown, don’t have a good handle on it. So that’s generally what I do now.