If someone found #66 and withdrew with an extremely high transaction fee say 10k USD and then within 1 minute the scammers find the private key with kangaroo and submit their withdrawal with lets say 100k USD fee! Would the scammers still get it? Cause this means all the lower bit range puzzles are useless to even attempt.
Correct, but I won't call it a "scammer", perhaps just a leech. And it won't be found within 1 minute. It will be found within a few seconds. The leech will still get 6 bitcoins, so even 200k RBF won't be too far fetched, as he'll get double his money back.
I feel sorry for people who enthusiastically tried puzzle 66 for many months or even a year or two, without realizing even if they found the private key there's no way in hell they will be able to withdraw it because unless you have 20/30/40k sitting around to gamble on the RBF lottery, you're not getting those funds.
The reason this did not happen before is because puzzle 65 and lower had very little to no reward money in it, so it was not worth the bidding war, but this all changes when the puzzle creator decided to put 6+ BTC in each puzzle. Now there's more people sitting and waiting with bots than people trying to solve.