Interesting. I have just a 10i5 NUC, so not the fastest, and never an issue with that (15 seconds for „the the“ was the worst it ever got). However, it will depend on other properties of the library and mine is probably not the most complex.
In any case, you surely are onto something. As Innuos products are generally considered underpowered and are therefore not supported by Roon as Roon Servers, it’s very possible that a demanding search like this brings them to their knees