If you think Bonanza, or the vast majority of Megaways games for that matter, is picking the result first and then choosing how to display it, then you're very much mistaken. It would be more difficult to develop the game like that, and it would be even more atrocious to play. You have, with the greatest respect, a very rudimentary and often cynical perception of how slots are put together server-side.
On each spin I think you'll find that the number of ways is randomly determined first, for example either by selecting the 'height' of each reel window (and therefore the number of symbols that will be show inside it), or by choosing one of a number of reel array combinations from a table - 233332, 333332... miss a few out to reduce the permutations... 777777.
Then it is likely that one of a number of different reelsets is chosen for the spin, again from a weighted table, depending on the number of ways in the spin. This is why you often don't win much from a 'max ways' spin - the game is selecting a low-paying reelset a lot of the time, otherwise you'd probably get 40 cascades every time that number of ways is selected.
Of course it's going to use a more generous reelset when the reels are 324 ways for example - otherwise you'll only ever get base game wins when a high number of ways is chosen and it will play like shit. You don't want the hit rate per spin to be too heavily-reliant on the number of ways chosen - it's all about making the game play nice.
I think you misunderstood me there. The pool of results as we know has many similar amounts, a favourite is 1.2x bet for example, a very common win on Bonanza as is say 0.1x for the 3@9s on one way. Of course the most common result is zero. I am suggesting that the result or spin yield is single entity attached to x amount of ways it will be displayed in according to the reel set. In other words it's a single RNG pull. As for eliminating some reel height permutations, I'm not sure it does. Once I had 100,842-ways, i.e. one symbol short of max ways. Exceedingly rare, only ever had it once in 7 years. I will say though that those combinations in excess of 60k ways are very seldom seen, but they're certainly there.
Another thing I've noticed is that in the base game the reel sets are consistent and don't appear to vary. I would say they are pretty long reels in terms of positions too, considering you can get 10 or 11 consecutive queens or other royals on them. Any weighting would occur in the pattern and construct of the reel strips which is why the same win amount can be produced by countless reel combinations/positions so the chances of getting say a thousand or more ways of a royal are vanishingly small.
As for the max MW spin, I would dispute your 'likely' suggestion because otherwise 40 tumbles would occur. Think about it - the art, the whole construct of the MW formula is the large and very clever reel strips. You don't need 'weighting' in the way you suggest. We already have evidence of this on other
BTG MW slots, where for example on MAX Megaways slot there is paucity of Queens on reel 1, Kings on reel 2 etc. therefore ensuring certain vast combinations of ways pertaining to a single symbol are next to impossible on a random basis - without any ways weighting. Another classic is the Rasputin game and Royal Mint where when I posted the intro videos before release, the comments and observations were cynical regarding the visually frustrating and very obvious prevalence of stacks of any particular symbol type on alternate reels.
Your comment regarding the 40 tumbles made me laugh because it had me thinking of the Thor free games round on Thunderstruck 2 where on about every tenth feature, the reel symbols would line up resulting in about 10 consecutive wins at 5x; you had hit the 'special' bonus lol. The reels trips on Bonanza for example would simply not allow that to happen.
I would love to see a genuine reel map for Bonanza, in fact I wonder if it's worth me trying to make one by playing it and putting the jigsaw together to see if my theory (same as your logic, I merely think it's 'likely' rather than knowing for sure) holds water.
Finally, it's worth considering the fact you can get a straight-in win of 4.8x on a poxy 1080-way spin with no winning tumble after removal, the rest being dross. The exact same win can occur on the max MW spin, just with far more dross in the picture. The real art of MW is that you can get a flat single-hit as just described, or the same win total but on more ways, this time constructed from 2 or 3 separate wins via tumbles. Megaways is just a visual illusion, almost a tautology in slotting terms.