I'm the one predicting Kluber, but I'm only citing stuff from the Red Sox site on mlb.com. Reportedly, he had a terrific bullpen session of just 30 pitches. And I cited that article because the news on Sale, Houck, and Whitlock is same-old, same-old: no earlier than August and maybe September.
Or put it this way. If Crawford has in fact found himself and if the same applies to Pivetta as a "bullpen starter," then Bello, Paxton, Crawford, and Pivetta might already be the best Sox rotation since, what, 2019?
Plus let's not forget that neither Houck nor Whitlock has been all that good at starting. Sale did have maybe 8 pretty good starts this season, but in the other 3 he gave up 7, 5, and 5 runs. Based on starts going back to 2017 when he faded in August/September, the truth is that he is as fragile as any pitcher I can remember.
So, realistically, waiting and hoping for the return of Sale, Houck, Whitlock, and Kluber is like waiting for godot.
Better is to keep the four healthy ones and trade the other four (if only they were tradeable).