Prevalent? Hardly.
My iPhone 15 Pro Max connects fine with many bluetooth devices.
People always complain about bluetooth, but there's no real evidence this is actually an existing hardware issue or consistent bug in iPhones and across many models.
Just because you have issues or you know people that have issues, does not mean everybody has them. What you read and hear is likely a very vocal minority of the billions of iPhones out there and in use.
Also, you may not be aware of this, but people also complained about Bluetooth issues with the iPhone 6 and even iPhone 11 back in the day just as much, but since you probably did not experience any, you simply were not aware they existed just like they do today.
And people will always complain when something goes wrong, but almost never say anything when it works fine, so you will always see more complaints than comments that it's working.
No such heavy documentation exists because no widespread bluetooth issue exists on iPhone models. People will say it's not working, then never come back when it does work.
Just to clarify, I'm not saying there no issues with bluetooth anywhere. That would be incredibly false. There's probably many, many issues around which will have varying causes and solutions and will affect various models of iPhone. I'm sure everybody will have a bluetooth issue at some point. The probability is very high with so many iPhones out there, if you taker a stroll around Android forums you'll probably find a ton of complaints about bluetooth issues there too.
What I'm saying is, just because people say they have issues, does not mean a device you own will have them. Nor is one model more likely to have them than any other.
If you can't connect a Bluetooth accessory to your iPhone or iPad - Apple Support