Does it? Roy Jones jr is the obvious example. A less obvious one is arguably the greatest light heavy weight of all times. Michael Spinks. This guy at 175 would have shattered Prime Roy Jones's jaw bone, he was a 6'3 monster at 175 with brutal power and immense skills. Yet, he is most known for being knocked out by a Prime Mike Tyson in 1 round. If he had retired after Holmes, he would be undefeated. That being said, it depends though, because Holyfield's legacy has not been tarnished and he fought on way too long. So maybe it depends how you lose.
Spinks didn't fight on too long. He quit the sport after the Tyson rapeing. But it doesn't affect it, Ezzard Charles is another example of fighting on too long yet he is still a top 10 P4P all time'er
You could probably make a case for Ali and Sugar Ray Leonard taking one or two fights too many but they are both in the top ten of all time, but it's slightly different when you take more than a handful. Even so, in the case of Jones Jr, in ten years time I'll still be looking back fondly at his ridiculous skillset in the late nineties and early 00's than now. Unless of course he's still fighting in 10 years
In every case I say no it does not effect a ATG fighters legacy if he fights on for too long with the exception of Roy Jones, in his case his weaknesses/faults that he had while he was in his prime were exposed when he was past prime.....His weaknesses of course with having a glass jaw and not fighting with the proper technique.
I believe it SHOULD have a negative affect if they're obviously way past their prime and continue to get knocked out. Why should they be allowed to do this? We should penalize them. Old fighters like Vitali, Bhop, Sergio, JMM, etc. have the amazing ability to fight at a high level. This should be a factor when judging their legacy. They should be allowed to gain major ground in the HOF/ATG rankings if they continue to accomplish great things while someone like Roy Jones continues to embarrass himself by getting Koed. Just because Roy was an unbelievable athlete at one point doesn't mean he was well-balanced; he could never fight at elite level at the age of 40 or older.
I hold the Tarver and Johnson losses against Roy... Nothing after those two... Still makes him ATG, and he was past his best.. But many great fighters have had great wins clearly past their best. Had Roy retired after Ruiz, he would be thought of much differently... He would have basically been 49-0, take away the DQ, 4 weight champion, and would be 10 years retired now, with that unbeatable aura still in tact.. He would be at least 20 spots higher.