That's not an argument that's going to work. It would work if the operator were letting everyone else away with doing this and choosing to persecute you, but that's not the case. Operators are enforcing these rules as a standard and making beneficial exceptions for those customers they actually view as being accidentally and harmlessly in breach. You agree to the terms at the point you accept the bonus. If the operator choose to give you a 'vip perk' by ignoring what they perceive as a genuinely mistaken violation that's at their discretion. They are giving a perk in these instances not stripping a right away. Your starting position is not being allowed to exceed the maximum wager. The perk is having an infraction ignored.
Which you won't win for the reasons I've already explained. It's very clearly a separate bet, both in its function and mathematically. If you don't agree with that you're welcome to your opinion, but I'm very confident that would be easily demonstrated within any courtroom environment.
It depends on the judge and how each side puts the argument. In Microgaming VP for example, the double up bet takes place from within the game, it is not "clear" that you have exited the game and entered into another wager. Consumer law in particular assumes the average consumer is not expected to have a degree in maths and an understanding of the operator's perspective. This has been designed specifically into consumer protection law as it is seen as a "David vs Goliath" battle, and this assumption of bias towards the "David" in the battle is designed to create a more level playing field so that the "Goliath" can't use it's deep pockets to hire the kind of legal teams a consumer would have no access to. It is entirely different from business law, where it is seen as a "Goliath vs Goliath" battle, and both sides are expected to have the depth of knowledge and legal advice needed to understand what they have signed up to.
It has had some unexpected consequences for businesses as some terms and conditions, no matter how watertight and well written, have been struck out in a consumer vs business battle because they are deemed to have been unfairly implemented. This means that a business might legally be in the right, but could actually lose in court when a consumer argues on the basis of unfairness.
If there have been 500+ complaints of extreme advantage taking of the gamble feature, it would be odd that not one would chance their luck taking this to the small claims court for a mere £60 and no costs if they lose. They are, after all, brazen enough to make a formal complaint to an ADR despite knowing full well that they are trying to exploit a loophole that the casino is certain to spot in a basic audit. These 500 must believe their arguments hold water otherwise they would not be so brazen as to make such an issue of it when they get caught.
What I expect would happen is that if they did make a claim, they would be paid off to discontinue unless they did so in such numbers that the operator decided it was worth the risk of losing to win a case and kill all further claims, and it would include a gagging clause to prevent them from revealing what the settlement was, or how easily they got it.
The UK banks were too scared to defend court cases over bank charges, and anyone who went that far saw the bank cave and offer them a refund of all charges just to prevent a case being lost in court. In the end, the matter was forced before a judge by the watchdog, and the banks WON, which was a surprise for many, but it proved all along that banks were in the right legally, if not morally, and had wasted millions giving out refunds before this.
Even now, charges can still be recovered under the "consumer must be treated fairly" principle, even though the banks won the legal battle in court to specify charges in their terms, and make them binding.
The moral of betting has always been that once accepted you pay up if you lose. If the bet is one you don't want to accept, you decline it, rather than take it and then refuse to honour it. Just because a computer is taking the bets rather than a human counter clerk doesn't excuse a morally questionable action, even if it can be justified on a legal basis. If a bookie has decided that they won't take bets over £10 from you, but staff make a mistake and accept your wager of £20, they are honour bound to eat the results of their mistake, even if they can legally wriggle out of paying up. It would be the same moral principle if they got rid of the staff and installed betting terminals instead, if the terminal took your bet for £20, the firm is expected to honour it, not claim that "staff error" meant that the terminal hadn't been programmed to limit bets to £10.
In the case of casinos, their short cut is that they have failed to program their bet acceptance limits into their "betting terminal", making it possible to strike a wager over the limit, and for the software to accept the bet and produce an outcome. This is sheer laziness on their part, it's certainly possible. This too could be argued to be an "unfair business practice", which is the consumers' torpedo that can sometimes sink the most watertight consumer contract.