The research on the UVB is still up in the air, which is why I recommended he go with it, its better to be safe. Providing D3 through the diet may be enough but I really have no idea.
For a smaller savannah a bask spot of 115-130F is definitely ok so long as they have access to a full body bask. The "one light bulb" approach is not sufficient. For any monitor over one foot I would recommend the higher temperatures (130-140F).
Tanks definitely can provide the proper gradient 80F-95F if you enclose them with plywood (I use the PE-1 and the accurite thermostats to measure heat). You will get heat "leakage" from the glass but this is solved by adding multiple flood lights. I do agree with you though, it is definitely easier to maintain that heat gradient the larger the cage is and the more the materiels resist heat escape.
Monitors are definitely tough as nails and you need only to look at the vast distribution of Varanids to understand that. You can find them on just about every continent in many different types of habitats. Yes, they all specialize in those environments as you would expect with natural selection but their builds are all relatively similar for a reason, because they work in a multitude of harsh environments. Again, I am not saying that it is ethical to exploit this toughness in captivity and slack up on the care of these animals.
I agree about your improper conditions paragraph as well. I just dont see how what I have recommended is improper conditions.
If we want to use the term "fish tank" to mean any glass enclosure then we have to universalize that completely. So, are the 20' x 20' glass enclosures at some of the major zoos incapable of providing a proper environment for Varanids?