You know, this whole Zelinsky White House mess reminds me about the story of Van Halen and the brown M&M's. In their tour contracts with venues they would specify that there had to be a bowl of M&M's in their room with all the brown M&M's removed. Early reporting on this portrayed the move as if it was the group just being overly demanding divas. In point of fact, it was a deliberate strategy they used to test whether the venues were really paying attention to the contract details. If the bowl wasn't there, or if the brown M&M's weren't removed, they knew to expect other problems that could interfere with their technically very demanding shows. The band didn't care about the M&M's themselves, they cared about the signal it sent about stuff that really was critical.
Zelensky failed the M&M test. It's not that what he said in the White House was all that bad in and of itself. But the fact that he couldn't just be polite, be thankful, not try to force Trump's hand when all of that would have been so easy, and wouldn't even require any concessions on his part... that's a sign that he's not ready to do what it takes to make negotiations successful. Either Zelensky is taking bad advice, or he doesn't understand the situation himself, and neither of those possibilities is a good sign. Failing at the easy stuff now suggests that he's going to fail at the hard stuff later, and that's why a smackdown was appropriate.