Well reasoned. Sometimes fans forget about the 'butterfly effect' of such a change. Fedr was dominating for years with the smaller racquet, so it's hard to let it go bc he would fear that it would take away the 'magic'. If I were him, I would find it hard to let go of the racquet that has brought me so much success, for so long. Could he do better with the current, larger one? Sure, but it's not that simple. The only real scenario where it 'might' improve his overall results is if he had started from juniors with it. But then again, the results could be much worse bc he would turn out to be a differnt player, thus possibly winning less. His slice likely would've been worse during his prime. But the slice he had with the smaller racquet was lethal in variety and putting players in awkward possitions (a weaker slice with the bigger racquet still gives Djokr fits today). No way to know the results for sure.We should be happy that he did change his racquet eventually. Sampras never did and regretted it afterwards. Federer did and had just enough time to prove that it affected his chances. The winning he did/does with it and that proof are the only things that matter in that regard.
Besides, I don't think that it would have helped him to win all that much more. Don't forget, in 2009 he reached all 4 Majors finals winning two of them and losing closely in 5 the other two. That sort of results would have been improbable in the case of him just changing his racquet. When he changed to his current racquet first (summer of 2013) he couldn't get it work at first (for many reasons), so he had to wait until the beginning of 2014 to try again. He then gradually improved and I reckon somewhere around Wimbledon 2014 it clicked for him. That is between 6 months and one year, depending from what starting point one counts. It almost certainly would have meant worse results in the first half of 2009 and possibly the entire 2009. We know that 2010 and 2013 wouldn't have been great years for him because of his health issues with or without the new racquet, so the only benefit from it outside of what he has experienced would have been in the 2011-2012 period. Considering Novak's ascendance in 2011, I think that RG2011 and maybe Wim2011 were on the cards. Maybe USO 2011 too. I don't see him winning AO 2012, nor RG 2012, he won Wim 2012 anyway, and peaked too early in the summer HC season, so not optimally prepared to take the USO.
In the end, it's a fun scenario to think about, but nothing would be guaranteed. Just look at his comeback in 2017. If he didn't keep trying to 'fail better' and went against the grain to come back after knee rehab, the racquet change might've proven fruitless/pointless. Both success/failure scenarios were possible when he swapped to the new racquet in 2014. As a Fedfan, I'm just glad to see it 'finally' paid off by winning AO17.