There is nothing "top-tier" about Strickland's striking.
His right hand is an absolute joke, he turns his elbow over and actually strikes with his thumb, and inside of his fist, rather than straight across the knuckles. A right cross your elbow should be out in your palm down. When Strickland throws rights they are looping in his thumb is pointed at the floor. Wonky, and lame AF, IMO.
Also, even his jab isn't that big of a deal. Go rewatch Round 4 and 5. His jab is pushed-out, slow AF, almost pawing.
When he throws his joke of a right hand, he's looking at the floor.
It was actually laughable, at the very end, because both guys were throwing sloppy, telegraphed looping right hands, both "hiding their heads" and looking at the floor, with both missing badly. It was almost a comedy watching the very end.
I do agree Sean has got a pretty good defense, but his striking is mediocre, slow and predictable.
But his overhand rights, while looking at the floor, are bottom-level amateurish, and nowhere near the realm of "top-tier."