Unupgraded Monogravity has the distinct honor of being the worst mono in the game. It's very slow and its control is, as you've noticed, susceptible to a lot of weaknesses. It can stallbreak decently, but even that falls victim to indirect CC like Lobo, Eternity, Antimatter, Reverse Time, Basilisk Blood, Freeze, Squid and more. Oty gets CC'd and though Gravity Pull is very effective, it has no second offensive use (like Drain Life).
A pure Armagio/Acc/Merc rush is the fastest Gravy can do, but other monos are significantly faster and more versatile (as the above-mentioned Phoenix+Fire Bolts, Adrenaline+Frogs, Monodark, Monoaether (Dims, Fractals, Psions)), even Toadfish+Ice Bolts.
Monodark handles Arena -much- better, assuming it's built well. As for Gravy, you should either focus on the Otys or just rush. Otys work best with Blessings when unupped, though to be honest while it's a decent enough deck its slowness isn't good for your electrum/hour. An optimized Gravy rush would look like this:
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4t5 55k 55k 55k 55k 55k 55k 55k 55k 55k 55k 55k 55k 55k 55l 55l 55m 55m 55m 55m 55n 55n 55n 55n 55n 55n 562 562 562 562 8pl
4 Armagios/Accs ensures you get both early in most games, and one of both is all you're going to need in most games. The rest provide a use for your early quanta. The only advantage this rush has over faster ones is that it resists killing CC decently, although Monofire and Monoaether are even better at both that and stallbreaking, sadly.
As for Catapult, Flying Titans is indeed probably the best unupped mostly Monogravy rush. It can be significantly faster than this standard rush and it stallbreaks very well.