Of course, but the point is there isn't anything suggesting he can't perform just as well on 3 days rest. Its common practice using #1 starters on 3 days rest in the playoffs. My preference would be to use him 3 times and not use Lester. I think that would give us the best chance of winning. He is a better pitcher than Lester. He has proven he can pitch well on 3 days rest. Whats to suggest that its a bad move?
I admit Farrell and Tito know far more than I do about Beckett, his healthy, etc. But he was VERY strong in game 5 against the Guardians. Whats to suggest that he would have done significantly worse on 1 day less rest? He certainly didn't say anything along the lines of him not feeling like he could pitch on 3 days rest.
The truth is its all speculation. Some want him to pitch 3 games, some want him to pitch 2. Its pure opinion. There really isn't any way to prove which is better. Beckett has done it in the past, but as you have said, that is a small sample size. But I guess a small sample size that suggests one thing is better than nothing that suggest the other...
I'd say if Beckett feels strong enough to pitch on 3 days rest, do it. If he doesn't, don't.
Either way, lets just win.