I think this is right. We don't yet know how things are going to pan out, and with hindsight, this could end up looking like a diplomatic masterstroke or a pathetic attempt at appeasement.
The difficulty for Starmer is that he doesn't really have any other hands to play at this point. The UK, even with European allies, doesn't have the might to stand up to the US and Russia, so seeking to influence is their only option.
Time will tell whether or not their influence is enough to achieve any positive impact, but for the time being, I think Starmer has played the hand that he was dealt as effectively as he could have done. He was clearly very well briefed and well rehearsed, and he had liaised closely with European allies to establish an agreed approach. We can only hope that, between them, they are able to steer Trump in a different direction from the one in which he appeared to be headed. Otherwise we're all fucked.