As many have said already, the only mistake - and I appreciate it was a doozy - was spending big on transfers that, putting it mildly, haven’t worked out and giving said players long contracts on the assumption that they wouldn’t be quite so catastrophic as they have. I don’t think anyone could have predicted back then how badly it’d all go, even if you were opposed to some or all of the transfers generally.
City didn’t have a stellar record the first time they splashed their new cash, nor did Chelsea; the main difference was their spending power was so far ahead of the rest that they could chuck more and more at it, and get genuinely world-class talent to make up for their mistakes.
Our cash injection came at a time when it merely put us on an even keel with the others. Players aren’t just attracted by money anymore because all PL teams have it, so it isn’t as simple as bringing in the best players because all the big PL teams will be competing with us, so even though we have a few bob relative to pre-Mosh Everton our scouting has to be as good if not better than the
Moyes days in order to unearth gems that a) want to play for us and b) are unlikely to have their heads turned by other suitors.
TL;DR: we’ve been garbage since Mosh but not because of Mosh. It’ll all turn out sound.