I cameup with the Mega sceptile set when it stats where confirmed.
View attachment 28134
252 spe/ 252 SpA/ 4 Atk
Jolly
Protect
Pursuit
giga drain
dragon pulse
This set is more of one to lead with. You mega then go for protect and then on the next turn you switch out. You then use this to come in on a electric attack get the plus 1. It seems strange but I've tested it on showdown and it works really well. But as soon as that electric attacker goes down it loses it effectiveness but it has a nice little niche.
It works really well from your experience. Your experience doesn't translate to the whole metagame, as it's too small a sample size.
Megas that use protect on the first turn are really obvious and can be played around by switching on the protect. If protect's been working for you, then it's either your opponent reasonably didn't expect it because you shouldn't be running it all, in which case Protect probably didn't help you that much anyway aside from stalling for an extra turn for like weather or trick room or something, or your opponent is inexperienced. Plus, Sceptile doesn't even really need the protect in the first place as it's already fast as hell on that first turn, the protect pretty much only allows you to mega evolve on Mega-Manectric. If Manectric is indeed a problem for your team, then sure, use protect, but it's honestly not hard accounting for it through teammates, and protect really doesn't have any other purpose on Sceptile in particular.
Pursuit is too specific to be a viable option over the many good moves that Sceptile can run, and the unboosted, uninvested base 110 Atk that you propose doesn't even make Sceptile that good a pursuit user to begin with. You waste those two move slots, which could be used to accompany Sceptile's great coverage and/or substitute.
Everything else you've said is not insightful at all, because you've basically regurgitated the most obvious points that everyone's been making since day one of Mega-Sceptile's announcement, but at least you're not wrong there. I'd also add, however, that you shouldn't switch in to electric attackers so freely, as most of them, including the aftermentioned Mega-Mane, have access to HP Ice or Ice Beam, and you can be damn sure that all of them will start running boltbeam or pseudoboltbeam for Sceptile. However, it still stands that Sceptile is at least an excellent check for a lot of electric attackers, especially rotom-W.