No, it's pretty good at what it does, although why the League would want yet another LRM boat when they already have the Apollo, the Trebuchet, the Archer, and the Longbow and I'm sure I'm forgetting some, boggles the mind. I'm a League, parking a fire lance behind a hill and indirect firing someone to death is our bread and butter, but dammit, we didn't need another LRM boat at the time, we needed a dual gauss trooper that didn't have tinfoil for armor. If you want bad design, the Marauder-9M. The -9M2 makes up for it, but the -9M hurt in how bad it is.
My first guess would be to make a cheaper, more easy to produce and field mech for fire support in the heavy bracket... but the Catapult only costs like 100k C-Bills more than the Yeoman and despite not having as many LRMs to spam per turn, it's much more mobile and versatile. And even though it doesn't have the "ubiquitous" quirk, it has been around for so long and fielded by so many armies, you should literally be able to buy Catapult spare parts in any given junkyard across the Inner Sphere. Fuck, when you buy a gallon of milk at the grocery store, you get a lower Catapult leg actuator as a bonus, I bet.
And speaking of the Trebuchet, I recently used it in BT2018 and I fell in love with that little rascal. Two LRM15s at 50 tons, that's a pretty neat package. Puts out as much indirect fire support as the Catapult C1 while being comparatively cheap... what's not to like?
I also like the Dervish, even though that one is a bit more of an allrounder with two LRM10s and two each of SRM2s and medium lasers to tell anyone to get lost that gets too close. Seems like a versatile platform, that can strike from afar, close in and then use those other weapons to ruin someone's day.
I honestly can't remember a single Canon 'Mech carrying ammo on its legs.
The Awesome 9M does. (But it's admittedly the only mech that I can remember atm, too.)
The 9M is an upgrade of the Awesome that uses Star League technologies and was introduced in 3049.[11] The 'Mech is built around a 320 Hermes XL Fusion engine, giving the 'Mech a top speed of 64.8 km/h. The heat sinks were upgraded to double heat sinks to allow this variant to be rearmed with three Fusigon Longtooth ER PPCs. The ER PPCs are backed up by two Hovertec Streak SRM-2s, split between the left arm and center torso and fed by one ton of reloads in the left leg, a Magna 400P Medium Pulse Laser also in the center torso, and a Diverse Optics Type 10 Small Pulse Laser in place of the head-mounted small laser. BV (1.0) = 1,469[5], BV (2.0) = 1,812
Just put the ammo literally anywhere else and this seems like a decent design. I mean, 3 ER PPCs, 2 Streak SRM2s and a bit of disco-death blinklights to soften up someone before giving them the pimphand of doom, that's always nice.
The "weapons can feed from ammo bins in any location" mechanic is a bit of a pet peeve of mine tbh. It makes the game a lot easier when it comes to ammo-management and mech design, but I just dislike this idea of having arm-mounted weapons that feed from ammo that's like strapped to the right ankle of a mech. Especially when the weapon is something super massive and the arm is way too thin to feasibly allow ammo to be transfered through by any means.
I honestly can't remember a single Canon 'Mech carrying ammo on its legs. I think it was a rule for the design team that the leg crits were reserved for heat sinks, a-pods, or Endo/Ferro-Fibrous dead space. Ammo in the head, on the other hand... I remember seeing a couple 'Mechs carrying that. As for MG ammo... I think the reasoning is something along the lines of "we got the space, this ammo is cheap, and that's that". Plus, IIRC in the fluff MG ammo isn't the memetic deathtrap it is in the game itself.
And it really shouldn't be. Even a full ton of .50 BMG rounds would go off more like the world's deadliest popcorn bag, as opposed to the sort of cataclysmic explosion you'd get from hitting an ammo bin containing 120 fully-loaded and fueled long-range missiles. Sure, half a ton of MG ammo would still mess up a torso, but it wouldn't send the reactor flying a hundred feet in the other direction.
Compare and contrast:
A whole lot of boolit, vs...
A single 500lb explody boi.
Well, you do have a point, but what you should not underestimate: Even if a ton (or half a ton) of MG ammo might not instantly ignite into one big explosion that turns a mech into two smoldering legs on different continents, seperated by an expanding mushroom cloud, burning ammo (as in your video) produces a shitton of fire and expanding gas.
The difference between the pile of ammo and a bomb: The bomb is built to ignite a as much of its explosives as possible while building up pressure within a hardened shell while the ammo was allowed to slowly burn and crackle merrily in the breeze.
When you confine those hot gases and fire from the machinegun ammo, you quickly end up with something that looks like
this. (Video can't be embedded

).
Sure, still not a huge explosion, but a fire like that will turn everything on the tank's inside into white-hot sludge. When shit goes south and the ammo cooks off really fast, it can easily launch the turret into the air like it was a pebble. There was an image of a wrecked tank in a Syrian city, it was literally just a floor plate with tanktracks to its sides and the entire area was covered in fist-sized chunks of armor pieces.
When an ammo cook-off is happening inside a closed, armored compartment, it either burns its way through and turns into a giant zippo or it just builds up pressure until it has enough force to make an opening.
To be fair, most places that buy Quickscell protects probably don't see battlemech raids very often. There are still better, low tech options, but maybe they just put all their money into really hot salespeople. Also generic corruption.
Maybe the low quality nature of their products made them end up not as badly hit during the succession wars. I mean, there's undoubtedly other targets more deserving to be put on the list of primary targets... and afaik, armies kind of like giving contracts to the lowest bidder, even if that ends up with a bit of a lackluster product. Of course, that doesn't apply to the corporations that make stealth bombers and guided missiles, but you need someone to manifacture raincoats and eating utensils for your soldiers and every now and then, the guys that make that shit also get a bit of a juicy contract to keep them around and they are allowed to make something more interesting than a toenail-clipper with integrated compass for GI John Doe.