I like to think that the Metamidion in competitive is only ever effective when its enemy pilots don't know what they are doing.
Yes, Metamidions are easy to learn ships.
No, Pyramidions are not really that "easy to maintain", because the main engineer is responsible for all engines and the armor/hull as well, you will never have engines if your hull gets damaged, unless you decide it's worth to move without pilot tools, even phoenix claw can destroy engines if nobody repairs them.
I would say "No" to making the Pyramidion's steering ability as bad or worse as the Mobula's or the Galleon's. Its turning abilities are already worse than any other not mentioned ship.
Anyway, the Metamidion in balance can be explained the following way:
Why is it so easy to kill with a Metamidion?
Because the Gatling and the Mortar do so much damage, they can kill even a Galleon with only 1 clip, if the Galleon was not being repaired.
How come a Metamidion gets kills when literally everything is supposed to beat it up?
Because guns that disable can miss. The reward of these guns is that they can disable their target indefinetely and this targeted component will never get the chance to be used again, gun or balloon, but if they miss, the risk is so high that all it takes is a Gatling and a Mortar to kill the ship of disable. Sometimes pilots whose crews are disabling quite well might get to comfortable and thus a single mistake can cost a ship.
Because out-turning a Pyramidion is entirely possible, but people forget how big gun arcs actually are. Out-cirlcling a Pyramidion is not that easy or even possible, because, who could have guessed, Phoenix Claw. However, the same goes for many other ships, some just need a second to get going, I mean the Galleon and the Mobula of course.
Because the game has more factors than a scenario of facing a Metamidion 1v1, head to head. Sometimes it sneaks into your side/behind and when you try to dodge upwards you might forget that while the Pyramidion may not be the fastest at vertical mobility, it is just fast enough to keep good enough gun arcs to shoot at the very bottom of your ship, which could be a spike of a Spire or a even a fin of a Goldfish, if the enemy pilot reacts slow enough. Sometimes its ally is there to support it, afterall, 1 gun that hits can change the entire engagement so it doesn't even have to be 2v1 the entire time, just softening the Metamidions opponent is good enough.
Because what is a Metamidion really good at? Keeping gun arcs with Phoenix claw in close range, while the altitude of the current engagement makes only slow changes.
Of course the Metamidion haa an easy time to kill something in close range, that is what that thing is good for! In every other scenario this ship is entirely useless! (Unless it isn't a Gat/Mortar front Pyramidion, but then it wouldn't be a Metamidion anymore.)
This also means that a rather large amount of factors has to be in the Metamidion's favor such as: Range, flawed enemy pilot's environmental awareness, imperfect disable ability of enemy gunners...
In conclusion:
That build relies on so many factors that nobody can really count on, which means that the Metamidion is in fact rather risky.
It is similar for the Goldfish: If you let it get as close to you as a Metamidion, you will very likely get some disable issues and even more so if the enemy fish decides to use one of its side guns.
Similar to long range: If you are getting beaten up in a long range engagement and you don't move out of range or behind cover, of course you will lose.
So, even if the steering ability of the Pyramidion were to be made worse, what is left for the ship to be good at? Suicide charges? Is that balance? Shouldn't then be the Mobula's vertical ability be nerfed too since it's better than any other ship and there is no hope for any ship to keep up with a Mobula especially when the Mobula decides to use hydrogen, which is a similar concept to almost no ship being able to stay out of arc of the Metamidion while in close range?