Is there any way we can tweak the wording of the off-topic reason used in this question (and other similar ones)?
This question appears to be off-topic because it is unlikely to help anybody else
seems like a non sequitur to me, and I think it might confuse users.
My rep isn't high enough to see the close options on this site, but I would suggest something like:
Questions that are specific to one website are discouraged because they are unlikely to help future visitors. Examples include individual website reviews for SEO purposes and general website troubleshooting.
I'm also not sure how the author of this particular question would be able to improve it to make it suitable. Perhaps it would be beneficial to have a community wiki "how can I diagnose problems with my website's loading speed?" question that we could point them to instead.
(As an aside, I wish the "too localised" close reason still existed. I can kind of see why it was dropped from Stack Overflow, but on this site I think it's a much better fit than "off topic" for questions like this.)