how could you justify not resolving it prior to release?
I'm not objecting to him addressing the lag, I'm objecting to him resolving it first. Until you've built something people want to play, addressing lag (and similar tertiary problems) is solving a hypothetical problem for a hypothetical player. And it may well be wasted effort, if you never nail the core product. But if you approach it from the other direction, as most game devs would, you know with a greater degree of certainty whether you should spend the time polishing. You either nail the core mechanics of the game and know that your polish work is justified in bringing the product to market, or you discover you don't have a product at all and avoid wasting your life solving imaginary problems.
Because even side projects are resource constrained. He missed a vacation with his wife. This is tragic, and happens all too often when you approach a product from a technical perspective prematurely.