Huh. I clearly didn't think of Synthesis, and I definitely didn't think of Weather Ball or Growth as I didn't remember Meganium getting those.
Welp, I'm wrong. Mega Sol is more useful than I thought.
I did note that Meganium doesn't have Growth in the main series titles, but that could possibly change in Champions (much like with Incineroar losing access to Knock Off). As for Weather Ball, Meganium does get it as a TM move in Scarlet/Violet through the DLC, and might keep it in Champions due to the synergy with Mega Sol.
Still, Dragonise...eeeeh. An uber-strong Giga Impact would be crazy, but for a spammable attack, Gatr doesn't really have much. Body Slam, I guess? Thrash > Outrage, for sure, if you don't mind being locked in + ending confusion. Double-Edge, if the recoil doesn't bother you. Regardless, it's still walled by Steel and nulled by Fairy, and doesn't do anything for his usual Water STAB, let alone coverage - unlike Sheer Force.
To be fair, the same could be argued regarding Mega Pinsir's Aerilate to some degrees. Even using its Z-A moveset at a base, there's not much Pinsir has that's better than just running Dual Wingbeat, and Aerilate doesn't do much for Pinsir's natural Bug STAB or coverage (in fact, it covers as much as any other Bug/Flying Pokemon).
As for the "doesn't do anything for his usual Water STAB" argument, the "-ilate/-erate" abilities don't particularly do much for a Pokemon's natural STAB, unless the ability targets the natural type
and the Pokemon have Normal moves that are better than moves that are naturally of the same type, such as in the case of Sylveon with Pixilate + Hyper Voice*. But Mega Feraligatr itself doesn't get very many options to properly utilize its additional typing naturally in the first place, so Dragonize gives it more options.
Fun fact: if its Mega Evolution had Sheer Power instead, then Breaking Swipe would become a 78 Power move (so 117 Power after factoring in STAB), but would lose the Attack drop (since Sheer Power negates secondary effects). Pretty sure Feraligatr would have better options for AoEs at that point, like 130 Power Earthquake. Dragonize at least gives Feraligatr the option running Breaking Swipe in Doubles to weaken the opposing team, alongside Body Slam or Double Edge for heavier targeted blows against Pokemon that resist Water.
*Honestly one of the most OP ability + move combinations in Pokemon history (most OP would be Pixilate + Hyper Beam if it weren't for the recharge turn). It out-damages both Moonblast
and Dazzling Gleam,
AND hits both opponents,
AND HITS THROUGH SUBSTITUTE. So you'd only run Moonblast or Dazzling Gleam for the times when Hyper Voice is either blocked by Soundproof (or reduced by Punk Rock, which doesn't matter since you're not keeping Sylveon around if Toxtricity shows up without you having a Ground move to hard counter it) or disabled by Throat Chop, neither of which come up too often.
Source
. I would've given Mega Meganium Serene Grace or Pixilate or something.
