Again this was also not about fobbing you off. It's important things are taken within the context that was said. It may well be myself who hasn't explained myself very well there, and can only apologise for that. While there are indeed clients with 25k pages, that doesn't make that normal use. It means simply that they exist, and these people aren't having issues. What i actually said there was
So by this, I mean you need to ensure if you have those kinds of topics and items which are going to take longer to run than say a topic with 10 pages, you need to ensure you have the resources and setup to run those things effectively. In this case, as pointed out by Matt above, running MySQL 8 will likely help, and indeed further to that, getting someone to debug the MySQL instance and web servers would be what you would need.