George Foreman might never have been champion. Unless he wins it from Norton. Patterson might have been champion again. (him v Ellis rematch might have been the only feasible fight in 1970 for the 'undisputed championship'). Ali would have been champion from 1971. Norton's the threat.
I don´t know what the most people think of this but for me his legacy became better because of his fights with Frazier
Yes, his legacy was improved by his fights with Frazier, but he would seem even more invincible had he not showed the weaknesses he showed with Frazier
How about the following scenario ? The WBA eliminations culminate with Jimmy Ellis winning the championship,as in real time. Jerry Quarry gets the WBC version. Ellis and Quarry have a rematch,this time for the whole ball of wax. Ellis wins again. Ali beats Ellis in 1971,about three months before he actually did. Muhammad beats a green George Foreman,and holds the title until 1973,when he loses to an unknownn named Ken Norton. Ali bests Norton in the rematch, then boxing history gets roughly back on track.