Mathematicians / folks knowledgeable on the subject - do you think Fermat had an error in his (lost) proof? Or that there exists a solution that perhaps is more straightforward than Wiles's?

My understanding is that Wiles had to use a ton of math (and invent some new math?) that had not yet been invented in Fermat's time.

One interesting thing of FLT is Wiles is on record as saying it opened the door (I think. This is from memory) to Langlands Program, a series of mathematical connections

Harder problems of course exist, Riemann Hypothesis et al but FLT still took hundreds of years to solve