The only reason Wlad saw the 6th round was Joshua came in at his heaviest weight and wasted a lot of energy after the knockdown. The hard truth is Klitschko posed more threat to 19 fight Joshua than does Wilder or Fury now. Since then Joshua has done about 30 rounds and has increased his knowledge in big fights. If Wilder were to knockdown Joshua and rush in , you might want to watch the Fury fight again and see where Wilder gets stunned rushing in, that's because he's not a calculated finisher. Joshua is the best finisher in the game , he will counter Wilder to death, and will corner Fury bc he actually cuts the ring off and unload on him at some point.
Wlad had more thudding, accumulation power. Comparable single punch power, but to the eye test, Wilder appears to have more. As is frequently the case, you just aren't being objective on Wilder. The sample size against top level opposition is obviously inadequate to offer a full comparison, although you are underestimating how cleanly Wlad caught Fury at several points of their fight. But, if you look at their resume's through 30 fights, Wlad had a marginally better quality of opposition, at the very best. His record was 29 and 1 with 26 kos, including one decision win and 5 fights that went beyond 4 rounds. Wilder was 30 and 0 with 30 ko's and no fight going beyond 4 rounds. There is certainly room for debate, but the eye test looks like Wilder has at least equivalent single shot sniper power. To my eyes it looks better than Wlad's, although again with Wlad having more thudding, accumulation power.