Great punchers can survive in any era, and I feel like Tank has certainly done enough to prove he's a great puncher. He's no Joe Louis, but he's good.
Not denying that Tank is a deadly puncher, but it takes more than having a great punch to beat an actual ATG and we have yet to see Tank beat any real elite fighters that pose a threat. Juan Manuel Marquez and Pernell Whitaker have had history of being put on their asses from fighters that didn't have Tank's power as well. Those 2 would have schooled Tank.
They definitely would've schooled him while the fight lasted but Tank, like you said, is an incredibly deadly puncher and could easily change the course of the fight with one bomb. I think this still applies to ATGs, although I'd give Sweet Pea a much better shot at lasting all 12 than Pac. That's the thing with punchers; you can school them while the fight is going on, but that bomb is still there. The only thing stopping me from giving this fight to Manny is how wild and chaotic he gets sometimes in his fights, the dude likes to brawl. He can pay for that against Tank.
The problem for Tank is that he overly relies on that power and can be outworked while still trying to look for that punch. Deontay Wilder was similar where he could end a fight at any given moment because he had the power to bail him out. A puncher's limitations will be exposed the moment he faces someone who isn't afraid of their power or is able to take their punches well. We've seen it happen many times in boxing. We'll see if Tank will come across his version of Tyson Fury, a guy that's smart but also tough.
I feel like it's a bit cruel to compare Tank to Wilder. Ouch! I think Tank definitely is reliant on his power, but he's certainly improved technically in his recent fights. He had smooth footwork against Garcia, but he was outworked in a few rounds in a similar fashion to how you're describing. I mean, Garcia was legit bullying Tank before he got caught in round 2.
I was merely giving an example, Tank is a better fighter than Wilder. There's been plenty of times when a puncher was being overwhelmed by a tougher and craftier fighter such as Mike McCallum against Julian Jackson and Salvador Sanchez against Danny Lopez. No doubt that Tank seems to have improved on his boxing game but he still has flaws that can be exposed by someone who is able to take his power. Like I said, beating an unproven fighter like Ryan Garcia does nothing on Tank's chances against any ATG fighters from the past. But we'll see how his career progresses.