Major merchants in the US do support UnionPay, even USPS(!) displays its logo. The problem used to be small/local merchants, but with the advent of modern PoS like square/clover it is getting better.
In what same way? Even registering a Wechat account is no trivial task, just look at all those ppl asking help scanning their signup codes. Suppose you did KYC and seasoned the acct enough to get it finally working, it is still limited to business codes (think of bigbox stores), not personal codes (think of farmers market, local mom-and-pop place, etc). The latter actually dominates the daily life in China.
IMO using V/M through wechat/alipay is like in the world you described and I was arguing UnionPay works in the US because ppl can buy gift cards at PO then use them at merchants, which is actually smoother comparing to this w/a business, but at the same time quite ridiculous.
unionpay uses pulse
The relationship between Tencent/Bytedance/Alibaba is what happens when there are no monopoly laws or they are ineffective: every company fighting tooth and nail to corner every market with a single "super-app". No specialization at all and many races to the bottom, like the recent war between Alibaba, JD and Meituan over instant delivery that made every company involved lose a lot of money.
In China, this kind of corporate driven censorship doesn't happen. Tech corporations like WeChat and Alipay don't control the payment routing that is run by the state's central network. A merchant just needs a bank account and a QR code, and any customer can use it to pay them. The private apps cannot arbitrarily decide to block a legal merchant based on corporate politics or moral stances.
By legal platforms or creators I suppose you mean the dispute between card processors and platforms like steam, pixiv, dslite, etc about nsfw contents like anime child porn? Those stuff are already banned in China long time ago.
To give a real example of how China bans stuff, take ByteDance as an example. It used to run a joke sharing app roughly translates into Subtle Jokes that is on par with TikTok in terms of popularity. Then one day CCP decided it did not like it, then poof it's gone overnight. The founder issued a public apology and promised to almost double their censorship department in the future. Comparing to the TikTok case in the US, we got what? The funny-yet-pathetic legal tic-tac-toeing of Singaporean-not-Chinese nonsense. There is just fundamental difference in the scale and efficiency of censorship.
A great example of this is how they handled digital payments. While Visa and Mastercard maintain a monopoly in the West, China faced a similar situation when private mobile payment systems began dominating the market. In response, the government stepped in and forced the ecosystem to open up to competitors.