I don’t feel this is a weak result. Consider if you built a new version that you _thought_ would perform much better, and then you found that it offered marginal-but-not-amazing improvement over the previous version. It’s likely that you will keep iterating. But in the meantime what do you do with your marginal performance gain? Do you offer it to customers or keep it secret? I can see arguments for both approaches, neither seems obviously wrong to me.
All that being said, I do think this could indicate that progress with the new ml approaches is slowing.
You better ship it
Then call it GPT 4.1 and allow version space for the next iteration.
I think the label V4.5 is giving the impression of more than marginal improvements.