I'm not sure what you're trying to say, or if you are sarcastic or dense here.

ARIA was very effective at using it's OP during lead-in and mood setting to the episode (it's one of the things ARIA became known for since few other anime were doing it at the time), which Mushoku Tensei also does. It makes an OP in the musical style that all of the respective songs share, more effective.

Nothing more than that.

Mieruko-chan's OP is just FUN. Amamiya Sora kills it on stuff like this.