To really keep sun out of your eyes, you need a physical shade. You can just buy one that sticks on with suction cups for the back.
I always tint my cars. I hate the heat. But that's really what tint is for. To block out heat and to give you some more privacy. Tint doesn't block out that much glare.
You have to find your sweet spot in terms of darkness. My sweet spot is about 20% (so I use the number reverse of what the law says; like if MD law says it needs to allow 35% light, then I'd refer that as 65% tint). Any darker than 20% and I think it gets too hard to see in dark or overcast lighting. Above that, and it doesn't provide as much privacy as I'd like.
If they need to remove windows, they're a bad installer. In some situations, they may remove interior body panelling but that tends to be quite rare as well. Most places, particularly ones that use computer cut film, just need to peel back the weather sealing at most. Generally, since it's on the inside of the car, they don't need to do that. Windows tend to have a black border so the tint just goes over that. For front side windows that do roll down, there's that flexible stuff that rubs along the windows and they generally just pull that back and the extra tint slips down in there.
Removing a window is just a really unnecessary step.
Dealers just outsource window tinting. No need to pay their middleman mark up.
Not all tint is the same. For example, since I'm kinda paranoid about heat, I pay about $600+ to tint 5 windows on my car. It's very special tint that very few places stock or install. Normal "good" tint runs about $200-250, altho I have seen not so great tint places charge that much for their crappy installation and their crap tint. The $100 for a car jobs use low end tint (may scratch, change color, etc) and tend to be cut to window shape free hand with a razor blade so it looks a little messy or might not cover all of the window (you see tiny spots of uncovered areas on the edges).
Kinda up to you to determine how much you wanna pay and for what quality of tint you want.