I'm not too disappointed, to be honest.
Yes, it was a little forced that both of them survived. I don't think it detracts from AoT's fame of killing anyone. Sasha died less than a year ago, after all.
What was harder to digest is that the bigger force at play, presumably Ymir, was introduced rather abruptly. Isayama is normally better at foreshadowing than this. I would have expected a more thorough preparation of readers for this reveal, other than vague allusions to Ymir having been in contact with the source of all life and the existence of paths connecting all Eldians. This is a deus ex machina in the most literal sense, since Ymir seems to have godlike powers.
But I don't find it impossible to digest. Titans are known for their regenerative abilities, so a mindless Titan being controlled by Ymir to fuse with Zeke and reconstitute his body is not really out of the realm of the possible for this series. I've seen much worse in manga, to be honest. This is on the same level of Edward Elric's exchanging his ability to use alchemy for Alphonse's life in FMA: I accepted it naturally, but some readers were outraged and said it came out of nowhere. So I don't mind if the readership is equally ambivalent this time.
If I distil the problem to its bare bones, I think what nettles me most is that there was no indication that Ymir remains as an existing entity with agency and a will operating in the story, and now an agenda that involves keeping Zeke alive. That was totally unannounced, unforeshadowed and hard to accept. But oh well.
Pieck is such a try-hard. Why does she think she can pull off restraining Eren of all people?