Also, measuring how well Shazam did is pretty pointless. Spectre falling down isn't indicative of how near defeat he is. No damage to his physical form is indicative of that. Black Adam blew through Spectre's face, him nor Shazam came close to winning those fights. The Shazam fight was also against a Spectre that had been in constant battle. Shit, in the first issue of the arc, he had just slaughtered like 700 mages simultaneously. Proceeded to stomp through Atlantis, took on the JSA and Thunderbolt, etc etc etc.
Nabu, the final guy he fought in the arc, was wondering why Spectre hadn't just destroyed him outright and had no doubts that he could. Spectre was simply doing things the hard way, because he wanted to.
People act like DOV was a random string of low showings that knocked him way down the powerhouse list, but in reality, everyone from the smallest mage to the highest gods and Lords of Order knew they were NOTHING compared to him and it was entirely hopeless, regardless of how much they fought he simply couldn't be defeated, only slow him down and hope someone would come up with something. And Spectre was giving them all drawn out battles simply because he felt like it. Didn't you find it odd that Temptest did about as well as Shazam in the Aquaman tie in!?
Eventually God himself had to stop The Spectre.
Thanos isn't this league, by a large step. Thanos is like a lit cheap hotel quality match to Spectre's big bang.