the way I read what you wrote, it seems like you think Zelensky's argument is bad and purely emotionally motivated, but the fact that Putin/Russia has broken agreements and ceasefires is a very valid concern, isn't it?
if the conference had ended without argument but behind the scenes Trump/Vance were setting up negotiations that go against Ukraine's interest, that would not have been a "win" for Zelensky other than in terms of a contest of popularity - but only the popularity among westerners who have no real personal stake in the conflict. it's Ukrainians and Russians who are dying on the front lines.
if the conference had ended without argument but behind the scenes Trump/Vance were setting up negotiations that go against Ukraine's interest, that would not have been a "win" for Zelensky other than in terms of a contest of popularity - but only the popularity among westerners who have no real personal stake in the conflict. it's Ukrainians and Russians who are dying on the front lines.