availability of parts/service are valid point
If you prefer manufacturers over manu-packers, then the following must must be true
anything Apeks other than their regulators
pretty much everything scubapro makes, they used to manufacture direct, but most is contracted now including most of the regulators which are made by Tabata, still speculation on whether or not the MK25 is done in house or not, but Tusa does have the license to make it for Halcyon
Everything Poseidon except their regulators/rebreathers, though parts of the breathers are contracted out
Most every computer ever made-the big run of Dive Rite Nitek Duo's/Cressi Archimede II and all the others were made by Seiko, SP and AUP contract theirs out. Dive Rite has the Nitek Q contracted out, Shearwater does make theirs in house
Most every wetsuit ever made-most are made by big wetsuit manufacturers, including 4th element and waterproof
Most BC's/BPW's made today-Halcyon, Deep Sea Supply, Oxycheq, and I think that's it actually mfg their wings in house, every one else contract mfg's, but no one except Oxycheq and Deep Sea Supply actually do the plates in house.
Nothing from Atomic other than regulators
Nothing from Zeagle except their BC's but even those are being partially outsourced right now
Can't use an SPG or a depth gauge as those all come out of the same factory in Italy
Can't use a hose that was bought from any company other than the hose manufacturer
Can't use a mask, no one actually makes those anymore, all done in Asia
No clips or bungee or anything, those have all passed through at least 2 hands before it got to you
No webbing either
There aren't a whole lot of manufacturers any more mate, but the fact is there is no way for a dive mfg to actually make money and build quality products if the did stuff in house and it is flat out idiotic to believe it is. Halcyon cuts and sews their wings in house sure, but the material is all brought it, their plates are done outside because they aren't a metal working shop, so they have a company that actually does stuff like that all day every day make the plates. They're cheaper and higher quality than if they did it in house. Dive Rite has all of their soft goods made at a company that does nothing but cut and sew, it is in the US which is better than Asia, but the fact is it is cheaper and better for them to not have the overhead because not a single manufacturer has enough volume to pump out product 24/7 and not be running tremendous amounts of inventory. It's far better for a "wing maker" to make wings to the specs of each of their customer and build them than it is to have the redundancy at each company. That makes it impossible for anyone but boutique brands to exist. Deep Sea Supply is one of the only ones, they do BC's and that's about it, Hog came about to buy gear from those manufacturers that everyone was buying from anyway, and offer it at reasonable prices because they were sick of the industry charging insane margins, don't be pigheaded and think that there is a single company out there that can offer a full line of gear that they actually make.
Not wanting to be argumentative, but you are either live under a rock and have no ideal what the actual state of the industry is as far as who actually makes what, or have bought the marketing bs and believe that some of the old manufacturers actually still manufacture and you get what you pay for. It's not a bad thing though, it pushes quality higher because you have one factory that does nothing but mill regulators, another that makes masks, another that cut and sews wings, if you brought it under one roof quality would suffer and cost would rise. Bad idea
If you had to build a kit that was actually only from manufacturers, then you'd be stuck with the following
no mask
no wetsuit
drysuits from either DUI, USIA, or a few others
Regulator from Apeks, Tusa, Atomic, or Poseidon
Backplate from Deep Sea Supply
Wing from DSS/Halcyon/Oxycheq
Fins from Scubapro
No booties
computer from Shearwater
have to find hoses and bolt snaps direct
Very limited selection if you actually want to go that route, and it is incredible expensive to do so.
You also need to return those fins and get a pair of proper Jet Fins if you want them to be from a manufacturer....