I can't think of a more perfectly constructed fighter in any weight class than Ali in 1967. (And he might have been even BETTER in 68-69 had he been allowed to continue his career--mind boggling!)
Ali fought and beat three men who are consensually seen by knowledgeable boxing fans as top ten in boxing history in Liston, Frazier and Foreman. going five and one against them. Also, three of those fights are seen as the greatest fights in heavyweight history. Factor in Quarry, Shavers, Lyle, Williams, Patterson, Ellis Norton and Bonevena men generally seen as in the top forty-fifty heavyweights in history. No one else even comes close to the competition he faced and the number of historical fights he had. He also matches up very favorably against any heavyweight in history when considering his size, speed, skill level, guile and mental toughness He is the G.O.A.T, the title he rightfully deserves .
About the same as Louis. Both are heavily overrated P4P compared to lighter fighers who consistently beat much better opposition then either fight despite not being ranked as high. But I think Ali should probably be higher just because he had better wins overall so around 15-20.
I'd say top 15. Greb, SRR, Armstrong, Langford, Charles, Benny, Pep, Moore and Ross are definitely over him imo. They just beat better opposition. 5-1 vs Liston, Foreman and Frazier sounds unbeatable when we're comparing Heavyweight resumes. But P4P ? The standards are much higher there. Greb beat Tunney, Walker, Rosenbloom, Dillon, Miske, Houck, Levinsky, Gibbons, Norfolk and Flowers Langford beat Gans, McFadden, Holly, Walcott, Blackburn, Ketchel, Wills, Jeannette, McVey, Smith, Flowers and Norfolk Robinson beat Gavilan, LaMotta, Angott, Zivic, Armstrong, Olson, Graziano, Basilio, Fullmer, Turpin and Servo Armstrong beat Ross, Ambers, Zivic, Arizmendi, Sarron, Bass, Angott, Joyce, Jenkins, Belloise, Wright and Garcia Charles beat Moore, Burley, Louis, Bivins, Marshall, Yarosz, Walcott, Christoforidis, Maxim, Ray and Satterfield Leonard beat Welsh, Britton, Tendler, Dundee, Kansas, Kilbane, Bartfield, Mitchell, White and Duffy Ross beat Canzoneri, McLarnin, Petrolle, Garcia, Battalino, Klick, Fuller and Ghounly Moore beat Williams, Johnson, Bivins, Marshall, Chase, Lytell, Olson, Valdes, Satterfield and Smith Pep beat Saddler, Wright, Bartolo, Terranova, Ortiz, Davis, DeMarco and Joyce (No seriously, look what these guys did. They're more impressive than the Folleys, Quarrys, Terrells, Bonavenas, Shavers and Lyles of the world) With the exception of Ross who is 4-1 vs top 30 P4P locks, both of whom I personally have in my top 20 (probably the only fighter ever to be able to say that), all of them pass Ali when it comes to depth as well. Ali has 39 wins over top 10 opposition. Robinson has 65. Armstrong has 64. Charles has 46. Pep and Moore have over 50 each (Pep was 54 and Moore was 56 last time I wrote them down, but I haven't done the full research yet). Greb had 39 in 1924-1926 alone (add HoFers and champs from before the ranking era and it's 63, add actual contenders too and it might as well be 100), Langford is similar, and when I did Leonard he had about 40 or so such elite as well. So Ali is solidly below those 9 for me, so he's #10 at best. I can hear the argument for Ross, but such results vs Canzoneri And McLarnin are unprecedented. After that he has to compete with Louis, Gans, Fitzsimmons, Walker, Duran and McFarland. I'm not sure I have him over all of these guys. I definitely have him over Louis, but I haven't sorted out where exactly I rank the rest. So I'll say top 15.
I think maybe 6 ft + HWs should be excluded P4P. Not that Ali isn't great P4P I just don't know how we weigh HW lifers over 6 ft with smaller guys cause this really isn't for them. Feels like every time this sort of prompt comes up putting a big guy anywhere near the top is wrong. Ali beating Liston and Foreman while underdog stories really aren't P4P or size based disadvantages. Ali was giving up a few pounds and no height. Being a underdog doesn't make it P4P.
NOTE: I miss understood the question, didn't realize we were discussing P4P , and not just the heavyweight division. Apologies. Ali should be the very 1st heavyweight to go on the P4P list, but he's not the P4P G.O.A.T It can reasonably be argued, he wasn't the P4P best of his own era. Especially when considering, Napoles, Olivares, Arguello, Monzon, Griffith and of course Duran were throwing hands in roughly the same era.
I think they all had better wins P4P then Ali. While great wins at HW I don't rank Liston, Foreman and Frazier high P4P. But you can agree to disagree that's just my personal take.
It's just unfair really, the guys at the lighter weights just have much more room to do great things than the Heavyweights.