Lucky Star and K-on for CGDCT
Evangelion for meta-commentary and deconstruction, to the point that future works that qualify often get called the “Evangelion of <genre>”
Fullmetal Alchemist Brotherhood and Attack on Titan for battle shounen
Bocchi the Rock for girls band anime, specifically
Lupin III: The Castle of Cagliostro for pretty much all of Ghibli
Akira for 90s anime
Not just SAO! I called out Rising of the Shield Hero because unfortunately it popularized the trope where an isekai protag goes and buys some slaves.
Isekai is a genre where every little gimmick from a work that gets a bit popular immediately becomes a micro-trend. The main character is an old guy! And he reincarnates into some weird thing that might not even be a life form! And he has cheat skills! And he got kicked out of the hero’s party! And he’s a villainess!
So a lot of works would have to be considered blueprints by that standard, I think.