Fair play on the two 4e codex options. During 3e, 3.5 and most of 4th however there were a number of competitive options, it's just that only a few were at the very pointy end. Look back in the archives here, and you'll find players who were winning major tournaments with orks - and with different lists too. I'd have to dig through the archives to find the specific lists they were running, it was a decade ago. Our list wasn't seen as a tournament staple, but players here were bringing back wins from 'Ard Boyz and similar. I know I could confidently field much more variety in 3.5 than I can now (though by the end of 3.5 we had three lists, and the six clan variants on the main Ork list, so there was that).
I suppose I can't really speak to 3 much. I was running Chaos Beakies back then and not orks. My friend who played orks didn't find they were a terrific play though but thats a sample size of one.
I'm finding it difficult to go all in on transports without being blown away whilst trying to pass bubblewrap. I'm finding 12 boyz just don't do enough to enemy squads, and even double charges don't hold up. 2 St4 hits on average per ork, is 1/3 of a dead beakie. Then they step backwards, their actual dakka fires, and the boyz vanish. I'm underwhelmed by trukkboyz this edition, but maybe your meta is different?
Fair. I'm yet to try flash gits, my first instinct was that they were mediocre. Nobs with runts and KFF might be okay. My few attempts with that failed, but harlequins are hardly normal and I was still getting the hand of 8th.
A unit of 12 ork shoota boyz piling out with their klaw nob will take down 3-4 beakies per turn. Even if you assume that unit is going to fall back, the trukk will have piled into another neighboring unit forcing THAT unit to fall back. Even if both fall back and other models near by turn their fire on the turkk and boyz, you have now taken two units out of the turn and required a minimum of two more to put their fire on the orks and trukk to avoid the two units doing the same thing next turn. If you have two trukk units hit the enemy line at the same time, there isn't likely to be enough Beakies unengaged to effectively take them all out. Combined with a wagon or two or even a gorkanaut, its a daunting task for beakie players to even consider trying to slow all that down. 'umies have a slightly easier time, but any units hitting end up mowing through those bubble wraps. Its all about the KFF coverage. Literally your entire army needs to be under KFF bubbles and a huge number of options open up.
Regarding nobz and flash gitz, running infantry heavy can be a very big problem for most builds to counter. They just can't deal with those nob aand flash git squads. The benefit of flash gitz is their massive amount of fire. Even on the turn they move, you get those 30 shots and up to 10 rerolls at 5+. When they stop, they get all that on a 4+. Badrukk is a great deal and when he is on the table, you get to reroll 1's then reroll another 10. Every other turn, you'll luck into another free round of shooting if you blast away with all three units every round.
As far as nobz go, with their 4+ and 5++ saves coupled with the bonus runt wounds, they are pretty durable now. I load them out heavy with klaws. Combined with 30 ork squads running beside them, there are too many bodies for most armies to handle. When running infantry hordes I often leave all vehicles at home and just green tides it. Most armies are taking loads of anti elite and anti vehicle options, which are wasted on green tides. Even nob squads are immune to anti elite because you will throw wounds on your ammo runts. If they concentrate on your nobz, the boyz will multicharge them. If they shoot the boyz, the nobz will rip apart anything they touch.