Truthfully it is impossible to say without knowing names and quotes. Are we talking Blue Elephant or Dusit Thani or Dao's Disastrous Dishes. To be honest the location doesn't sound promising unless Dao charges low and sorts the visa issues.
Wow! Clear advice is simply unavailable for the way so many people actually work. This becomes a great indication of the art of the possible, hugely valuable - but, of course, what happened in Phnom Penh isn't necessarily an indication for elsewhere, the usual problem of Thai officialdom.
I take your point but it is a discussion best not begun or we will move toward looking at educational standards among arriving expats. I mean formal education there. But you could argue that as irrelevant and the thing to focus on is "street" navigational skills, but those have collapsed too.
Good to have up to date and specific information. What happened even a few years back can be of no relevance. I have certainly never paid to open an account, but most of my accounts were set up years back. That said one was set up in 2022 and no issues. But on all occasions all my ducks were in a row and no stupidities like tourist visas, etc. Something was interesting about 2022, simply that the bank was a very unusual choice. Why do people keep going to banks that we have heard of over and over again refusing? Yes, different officers, different days is an argument, just as with Immigration, but constant rejection is a fair indication so why try bank X?
How long ago? Things have changed very rapidly of late, including some new banking rules coming into play. Agents are the way now, no matter how much shoe leather you are willing to put into saving say 3,500 -5,000. Maybe 8-10K in Bangkok.
On the address. Agents have relationships where they have relationships. You change the address subsequently in TM30 registration, then follow that through on your TM47s (90-Day Reporting). Finding an agent to get a bank account for you locally may be more difficult but important as you don't want to find yourself paying out province bank charges often and change of account province isn't regularised in the way the Immigration procedures just described are.
A very weird post in many ways. The reasons for Thailand being difficult are system fragmentation, that different immigration offices act differently. Simple. Though not business friendly is legislatively ingrained. So why come here? Quite why other countries in the region are generally easier is open to question, but if you want business friendly then it isn't just a case of Malaysia, but Cambodia and Vietnam too, especially Cambodia.
There is no universal answer. It depends on which UK bank. You won't successfully generalise. Beyond which bank it depends whether you keep a UK address or try to operate from the overseas one. Finally there is a question of whether the account is actually being operated or is a sum of money left there to keep the account open - an active account actually matters. Activiy is simply shown by number of movements into and out of the account, but it is said that a large account balance helps too.