As 1 and 2? Hell no. Truly you can count the number of great wins Marciano has on one hand. He has a lot of wins over older guys. The thing is he was unfortunately in between great eras, boxing gets these transitional eras, Larry Holmes was in a similar time (Its interesting that both have the 2 most impressive win streaks at hw, 49 and 48 respectively.) Where you just had an amazing era, but the legends are starting to fade and not enough new greats have come through. We have it like that now... only 100x worse, and after 10 years of it; no end in sight
Taking that into account, Marciano barely makes my top 10. I still think he was amazing, and for a guy who looked so clumsy he was a bit of a genius. But its hard to rank him high based on who he beat.
Dempsey was great, but not number 2... 6-10 id say. He was also not in the best era, only around the title picture after Jack Johnson's reign. I think if he had been around 5-10 years before he would of ended up another white hope to fall to Johnson.
Like Liza said all top 10 lists will be biased in some shape or form, everyone has a different opinion on who was the 'best'. You could probably count the same great wins on your hands with a couple other guys in the top ten, etc for me Liston, Tyson both are overrated big punchers. Tyson beat a handful of good fighters, and a few guys past their primes. Liston beat Patterson twice with two impressive KOs, but I still think he lacked in the skill area, which was exposed once he fought a guy who could take a punch.
I think my list would change again if I did it again, as I've had more time to think about it. Evanader, Johnson, Norton would all move up a couple spots, and guys like Liston, Tyson and Rocky would all probably move further down the list a little, Rocky would probably fall to 9th, I know that one for certain.
But again I based my list of skill level, impact on the sport, title reign, quality of opponents, and a little of who I thought could beat who had they been able to fight now.
And Liza, I think the CW division has a lot of talented guys that are often overlooked, I think a big reason for this is because the lack of great American prospects, its the same way most people hate on the HW imo.
Speaking of HW again What everyone think of Deontay Wilder? The guy has a lot of power and can cause some trouble for the Klitschkos. I'd like to see Wilder fight a someone who is durable like Arreola, or even put him against a guy like Fury, or even one of the other big up and coming prospects like Stivern, Leapai.
Also Bresk, Sweet pea will always be a favourite of mine too.