I think that guy has been living an extremely sheltered life, but it is understandable why he felt like that. He had no idea what he was doing, didn't researched his destination prior to visiting, etc. That's the only way someone can say there's nothing to see or do in Santiago. Centro Le?n, the Monument, the Tobacco Museum are some of the things that pop into my head of places a tourist should be, at very least, aware they exist.
He talked about searching for architecture or something identifiable to the city and he couldn't find any. Yet, there he was in the center of Santiago, which is the neighborhood with perhaps the most exciting architectural mixture in the city. There are neoclassical buildings (the post office is a good example), elegant victorian houses, Spanish revival, brutalist, modern and many other styles; and yes, the usual bland boxes as well. Unless he was expecting beaux arts type of buildings all over the place -which DR only has like 3 nationwide-, I really don't know why he even mentioned there's no architecture.
The poverty, well, he bumped into a marginalized neighborhood and probably the old p?blicos didn't give him a good vibe. In a good deal of Santiago you actually have to search the marginalized areas in order to see them.
The garbage situation in Santiago isn't as bad as he claims, except in certain areas. Apparently, that's where he decided to walk through.
The smell of car exhaust is true, not just in Santiago but practically nationwide. It takes roughly 3 or 4 days before people stop noticing it. There's nothing that can be done about that, as well as with the noise.
He was just completely ignorant of where he was going and didn't do his homework of what to see, do, and where to travel in the city. He even mentioned Santo Domingo and beach in the same sentence, a sign that he either stayed in Boca Chica (judging by his reaction to Santiago, I don't think so) or Juan Dolio and thought he was in SD.
By looking at the small clips of video that he took in the streets, my guess is that he simply walked around the Center, then on the 27 de Febrero heading towards the west, as if you're going to Navarrete and that part of town is not particularly the nicest area, but I don't consider that to be terribly bad. Those areas are mostly a mixture of middle class and working class neighborhoods. However, it is different from the eastern part of the city and I'm sure he would had felt much more comfortable in that area, which apparently he didn't bothered to visit.
All in all, I think he was just didn't do his homework and then made one bad decision after another, as far as his standards are concerned. Another thing to take into consideration is that he, apparently, was walking all over the place and that greatly limits how much of the city anyone can cover during any visit. I'm guessing he didn't took a taxi (to where? He didn't even know what there's to see!) and much less rented a car. Never looked at a map or even asked at the hotel what is there to see and do.
For the most part, it's his fault for having such a bad time.