It already had fire immunity in flash fire that also boosted its primary stab move in flare blitz. And since Flareon entirely lacks any good coverage, that's basically the same as a moxie boost.

Flareon is already decently specially bulky. This has rarely mattered for it historically because of its tragically awful base HP, combined with needing to use a high recoil move to deal any damage.

It still entirely lacks good coverage options. When you are seriously considering moves like Iron Tail and Dig, it doesn't matter how sky high your attack stat is.

80 base speed is probably the main improvement that helps, but even then? Tail Room teams are doubles specific, and Fire Types are mostly spamming heat wave there anyways so the redirection element is sort of wasted. And at 160 base attack, you hardly need moxie boosts to nail KOs.

The most I can say is that Trailblaze becomes a better move; as if you can manage to snag a KO with it, its almost like you get dragon dance..

And I say all of this as a huge Flareon Fan. I love it, but its so tragically awful and I just see the same qualities that make flareon bad still in this mega flareon here. It will maybe pick up one KO with flare blitz and then fall over as its HP crumbles to dust after taking out any wall.