Not sure if you are being disingenuous or you really don't understand. I'll give you the benefit of the doubt and assume your stupid.
A few things:
1) blocks can be anywhere from a second to well over an hour, so no, your stats are only theoretical expectations.
2) XT being 75% doesn't mean it can't lose - there's a reason why core uses higher than 75% ...
3) 'XT' have stated they will use block markers to force people to stay on XT and not switch to Core, if however, Core is above 50% and gets ahead of XT, everyone on XT will be royally screwed
4) It only takes one 'XT only' block to be mined to keep everyone using XT off Core

but more importantly, XT wont happen.