I'm not talking about film quality. I'm talking about the health of the larger MCU as a franchise, which is clearly not doing hot at all. Black Panther and Guardians got people to go see those specific (really good) movies, but weren't able to reignite the fervor that the MCU had in it's prime. We've seen the lowest numbers in MCU history (The Marvels and Secret Invasion) after BP/GotG, and even the really good stuff like Loki is doing way worse than S1 just a few years ago.
I don't call Strange and Thor flops because they didn't make money; they made significant amounts of money and lots of people went to see them. Maybe flop is the wrong term to use, but I consider them "flops" because they did not satisfy their audiences or leave them wanting more afterwards. I think Strange and Thor were a significant fall-off point because despite Black Panther and Guardians being great, the MCU spell was broken and people became way more wary of going out to see an MCU film in theatres after that. There was a lot of hype going into DS/GotG that ended up swiftly evaporating for films like Ant-Man.
Pre-Thor 4, even bad movies were massive box office success stories; Post-Thor 4, even good movies aren't absolutely demolishing box offices like they used to.