Curve have stated they ‘cover their costs’ on transaction fees, so I’m not sure they’re losing money on these transactions.
While GBIT is a nice feature, it’s also a function that Curve basically have to offer. I bet the majority of users actively using >1 card have at least once charged something to the wrong card, and used GBIT to fix it.
Skimming of HMRC transactions just feels wrong - on a par with AmEx blocking Curve. What’s next - 1% charge on Waitrose transactions because you’d shop at Lidl if you couldn’t afford it?
Free for metal holders isn’t really a ‘compromise’ - if you don’t already have Metal, there’s a simple cost/benefit analysis - and I suspect very few people make significantly more than £15/month extra cashback by using Curve to pay their tax bill.