Times have changed mate, crypto regulations and compliance is a thing and when an exchange openly bycot regulations despite restrictions, then it's brings questions about their legitimacy imo.... About the other matter, maybe he uses the platform and just sharing his experience/tips which is normal buddy.
Their legitimacy might be questioned based on their compliance, it seems that they're not compliant at all and this is their business. If OFAC has already given the sanction for their currency to be traded but BingX isn't compliant at all, that's their problem and they made themselves aware of future sanctions that will hit the exchange itself. But I think that this won't be a problem anymore globally, many exchanged have stopped their support here and there and even had hard time complying in US' standards. And as for the basis of these sanctions from US, they might or might not be obliged to follow and will just leave the region that they're supporting covered by the US laws. Anyway, if Bingx doesn't care at all, why should we be?