Sounds like the post of someone who recently got their first snake, probably has very little experience, and has an axe to grind for some reason.
I'm not going to endorse his handling, but I think we're just getting a little bitchy if we attack a foreigner because we don't like his handling technique. There are better things in this world than how someone else handles. Some are better, some are worse, some are just different, whatever. I am certainly more gentle than the average keeper, he is probably a bit more rough, but his animals thrive, we can't argue with the results. They can't be too stressed. Don't lose sleep over it. The medical system over there is not socialised like in Australia, so if he's bitten it's his problem. Much more than in Australia, his body, his choice. And yes, some snakes are more prone to biting than others. If him getting bitten by tree boas gives people the message that tree boas are not a good snake if you want something to handle without being bitten, I'm struggling to see a problem.
Snakes don't need human interaction. They don't benefit from it. Don't lose sleep over this. After keeping snakes for most of my life (I'm 40 next month, ouch!), dealing with a wide range of species from elapids, pythons, boas, colubrids, vipers (no, none of the exotics have been in Australia) I've been surprised at what works best for most species. My first enclosure had rocks and wood and fancy substrate and three heat sources etc etc, and it worked really badly. Of all the different methods I've tried, the one which snakes get feeding best in, which presumably means the snakes are happiest in, is even more simple than what Brian uses! I don't even generally describe it to people, partly because they'll think I'm lying and partly because it does take a little more skill to get right, but the next best thing is a small tub (smaller than recommended so they feel secure), a water bowl, paper substrate and yep, no hide. For newbies who don't fully understand the situation and for whom I don't have an hour or two explaining things to, a larger tub with a hide usually works okay. And also, this is what everyone else recommends so if I don't say anything unconventional I can't be blamed when things go wrong. But if my goal is to make a snake as happy as possible to get it to feed as well as I can, I will use a setup similar to Brian's but slightly more simple.
I'm not sure about his quarantine situation. I personally think it's important to quarantine, but in all the years I've been interacting with reptile people, I've met maybe half a dozen who actually do practice quarantine. Many many claim to, but most of them only pay lip service, most of the rest try but don't actually achieve anything (very few people understand what genuine quarantine involves), and just a very few actually practice it. I personally put a huge amount of effort into quarantine, but if Brian doesn't it just means he's like virtually everyone else.
Obviously someone with thousands of animals will have had animals die. You won't find anyone in the world who has kept thousands of animals and had none die. I've had thousands of snakes and I've had snakes die. I've never had a disease outbreak.
He doesn't respond well to haters? Wow, unlike everyone else who sends them chocolates and flowers and gift hampers? C'mon, what do you expect? He's actually a really lovely guy. He's not perfect, neither am I, neither are you, no one is.
As Brian would say, make today awesome and please do something kind for someone today