Well, not sure why you think TEK is so tedious/difficult to obtain.
Let me tell you about our MEGA - Read 3 (Three) person tribe.
We constantly have lots of Element available to us. We have countless transmitters, a replicator on every map. A cloning chamber on one map, about to make a second one this weekend to clone Basilisks, Crabs etc. An abundance of Tek dino gates.
An entire structure made of TEK. 45x45 base platform. so it's not a small thing.
50+ Tek troughs, a dozen or so Tek generators, 4 or 5 Tek teleport pads.
Rex's getting wiped? Sure it's a thing. But we plan accordingly and have backups waiting.
We are in process of building a facility to house our Boss Rex army, scaled to hold upwards of 450+ of them. And have 150+ Boss Rexes ready to go as needed (Due to the Issues you mention). As soon as the structure is done we will be hatching 200+ more Rex's to fill it. We have a set of Rex's on Island for fights and a set on the Rag map for fights.
We have completed all Boss fights on all difficulties (Have not done Alpha Rag, no need to do so, is only reason). Completed Alpha Dragon on Island back in December, most likely will not be doing that again anytime soon, No need to, is why.
Takes 25 minutes to set up and run an Alpha Broodmother or Alpha Monkey. We have enough tribute to run about 100 Alpha Broods, running low on Monkey tribute. So we now pretty much run Alpha Brood exclusively. That's 84 Element every day if needed.
All of this with a 3 man tribe, not what I would call Alpha or anything near it, and before you say we have no life, we all have full-time jobs.
As for the gear, we do have some TEK gear, Boots (They Rock), Helmets are great for TEK Cave, Chest also. We do not wear these at all times. But we are about to do so with the boots, cause they rock.
AB Element is easy enough to make and we use that to supplement what we might fall short of elsewhere, not transferable, true, but we craft it into what we need then transfer it off.
Your thoughts are not so much a matter if it is doable/feasible for small tribes. It depends on what your tribe wants to do, plan for it and getting it done, that is how we have done it. Yeah, the fights are tedious, but so what, so are meat runs to raise Dino's, but you still do that when you need it, countless more times than Boss fights happen.
We used to trap the Dragon on Legacy, but since Retail release, not once have we trapped the dragon.
Just my 2 cents on the subject.