He has solid subs but in no way is he the bjj threat of Mir, let alone a world champ level guy like Werdum. There are idiots that point to Aspinall losing via heel hook 10 years ago in his 4th pro fight as evidence that his grappling sucks. Quite frankly, those morons are my favorite kind because they help me get more attractive betting lines via their ignorance. The reality is that from the (albeit limited) evidence we have, Aspinall is a very much above average HW grappler, but can't be mentioned with the elite HW grapplers we've seen.
His striking is a different story. His speed is what mostly separates him. Both at range and in the pocket. If you watch what happens when guys throw at him and then try to reset, that's where it's most obvious. They just aren't used to having strikes get there so quickly as they reset. The Pav KO is a perfect example. Pav throws and Tom slips and his counter hits the side of Pav's head so fast, it's just not a shot that HW's land so quickly in that spot. The Blaydes KO too. Blaydes throws an overhand and at the distance he's at, he thinks he's safe. Tom's counter just gets there quicker than what other HW's are capable of.
Does he have the raw power of Ngannou? Probably not, nobody in MMA does. But that doesn't matter all that much, you only need enough power to put the other guy away and if your punches land and theirs don't, how hard they hit is irrelevant. Pav honestly probably has more raw power than Aspinall. Meant nothing at all when they fought.