There's always been a problem with foreign credit cards in China. Places show that VISA logo, yet when it comes time to pay, it turns out the VISA logo is there just to be stylish, or the machine is broken, or they only take "domestic" VISA cards. In part I blame the VISA people for creating the "China-Only" VISA card: a VISA logo in a shop should mean the place takes any card with a matching logo.
That said, I too think restaurants and such are starting to force customers to use QR code payment methods instead of credit cards. No doubt it comes down to money: fees on QR code payments are infinitesimal compared with credit card fees. It's just money down the drain when a customer pulls out a credit card to pay.
But there seem to be new regulations which limit the amount you can spend each day using a QR code, 500 or 1000 RMB depending, I believe. So this may force more places to keep open other payment options.
As to Wechat and Alipay versus UnionPay, I think the Chinese government -- which does like to be in control, doesn't it -- isn't happy that two private companies now control such a large slice of the payments pie. (UnionPay, which is owned by the large banks, effectively operates as a state-owned enterprise.) And the government can use its regulatory power to harness Wechat and Alipay, as it's recently done with those new payment limits.
In any event, for foreigners the point isn't whether UnionPay does or not grab a big share of QR code payments. From a foreigner's standpoint, all that matters is that UnionPay becomes more or less as accepted as Wechat and Alipay, since setting up UnionPay is so simple.
There is a China only Visa? That seems like it debases the brand.