I notice you didn’t compare Rey with Anakin winning the podrace (no training), or with Luke using the Force to make a shot “that’s one in a million” (no training) as that would rather count against your Mary Sue argument.

Rather you go on about Luke having had a hard life - in fact Rey has had a far harder life than Luke. She raised herself as a scavenger and lived alone in a shanty. Luke had a relatively secure home life and upbringing. When Rey does finally make a connection to a Father figure that she has desperately wanted she sees him killed before her eyes… I’d say that qualifies.