Sorry to hear that your TBH colony perished. But I'd like to comment on your assertions.
1. You had cross combing because your guides were not good enough. Had you have spotted this earlier you could have tried different guides and got the bees to follow them. I fully agree that comb needs to be inspected. Comb can easily be cut were joined to the side of the hive. I have two TBHs and have little difficulty inspecting the comb. I'd rather have the bees build their own comb rather than using contaminated foundation.
2. I agree. But the bees will propolise any small gaps anyway. And if the gap is really big you could always use a little imagination and fill the gap.
3. There are many other treatments for varroa than thymol. I know sugar dusting is oft mentioned. Also it's just as easy as a traditional hive to hang any impregnated strips on the bars.
4. Depends on the feeder. I have built feeders into my followers. Or you can just use a tray with syrup and a landing slope for the bees and place under the colony. It's not rocket science.
TBHs are perfect for beginners. If you can put shelves up you can build a TBH and keep bees for a fraction of the cost and paraphanlia of "conventional" beekeeping.
I've worked on Nationals and TBHs and I prefer TBHs for their simplicity, cost and lack of foundation.