It isn't unprecedented to have a late round pick contribute to a playoff team. Immanuel Quickley did it last year with the Knicks.
Butler, if healthy, is an absolute steal in this draft and can contribute to just about any team. His whole negative is his health status.
McBride is already a top rate NBA defender with a 40+% from 3. He can contribute to just about any team as well.
Both of these guys, I predict, will be better than Landry. So yes, I'd rather have one of them AND Carter over Landry.
Guys like Ayo might take time to develop and are less like to show this year.
Also, while I'm not over the moon on the trade, I can't wait to see what Monty does with Landry. Monty has made every player I can think of play better under his tutelage. Landry is a hungry player who wants to help his team and he'll be a perfect fit here. I expect Landry to have his best year as a pro next year.
Butler had heart issues. That is serious enough I'd rather not gamble on. Go with the sure thing in Shamet. If it was another health issue, maybe, but heart issues aren't just a health issue teams take lightly.