Is the gap between A-class healers and B-class healers really that large?

So I just finished episode 5 of season 2 and the scene where the A-class healer literally helps one of the damage dealer hunter “grow back an arm” reminded me of Joohee during the double dungeon raid in the first few chapters of the series. Joohee couldn’t do much for Jinwoo’s cut off foot and started coughing up blood when she overexerted herself, but this A-class healer grew back an entire arm in a matter of seconds like it was nothing?? Is the gap between different classes really that large?