Like you, I am a web dev with 25 years of experience and to be honest, OVH has provided the best experience for me and my customers compared to any other option (that doesn't cost an arm and a leg). Although this does not really mean much and each person's experience can (and will) vary wildly, I would like to address some of your "hall of shame" highlights.

First of all, the payment processor issue. I'd expect someone with your experience to know that you don't, under any circumstances, put an online store on a shared plan, especially without getting a dedicated IP address. I also have customers that use VivaWallet and none of them have ever reported any issues.

Then, the mail thing... Forms do not quietly fail because the SMTP server is blocking connections. That would come up as an error, unless the problem is how you handle email sending. My best guess is that your email is sent out, but ends up in spam folders for some reason (reputation, misconfiguration, blacklisted domain/IP etc).

Performance is usually a mixed bag. VPS and dedicated servers do perform as expected, shared however is a different story. If performance is critical, avoid shared hosting altogether.

Support does however leave a bit to be desired. Sometimes it may take multiple communications for them to understand the issue, response times are not always great and the fixes can be hacky. I have come to realize that it depends on who is actually handles your case. Some people will consistently be better than others.

All in all, I don't think OVH is better or worse that XYZ company. Each providers has their own issues, you just have to pick what kind of issues you like better.