"which" and "that" are relative pronouns. "As" is a conjunction and it means "since/because". You could replace "as" with "which" o "that" but you would change the meaning of the sentence and I think you should remove "such". -"He never hesitates to make such criticisms as are considered helpful to others": it means he makes criticisms because people think they are helpful. It's the reason why he makes them. -"He never hesitates to make criticisms which/that are considered helpful to others": he only makes certain types of criticisms, only the ones that are considered helpful not the others. You could leave "such" in a non-defining relative clause: -He never hesitates to make such criticisms, which are considered helpful to others: it simply means that people think those criticism are helpful, but it doesn't affect the subject. The fact that he makes them and that the people consider them helpul are not related (with "as" they are). I hope that's correct. If there is any mistake, please correct me.

yes ok

'He never hesitates to make such criticisms, which are considered helpful to others.' Hope this helps?