1) Depends on what you're doing. The queue times are, obviously, at the mercy of other people playing tank and healer classes. If you're playing in prime-time for your data center, and you're doing something that a large number of people will cycle in and out of (leveling dungeons, level-cap dungeons, etc.), the queue times aren't bad, in my opinion. Queuing for roulettes of any kind almost never takes very long. I've been spamming the lv71~79 dungeons for exp this past week, and I've been surprised that the queues have often been less than 5 minutes.
Unfortunately, if you're doing certain types of older content, queue times may take a while. For example, if you wanted to run through an Alexander raid, you'd be at the mercy of people queuing for Duty Roulette: Normal Raids, which might take a while. That roulette would first fill up the queues for anyone else that queued for other raids before you did, so it could take a while.
2) I do, personally, but I'll admit that without some sort of DPS meter, it can difficult to see your contribution other than just knowing that you're hopefully doing more damage than the tanks/healers. Since Shadowbringers took away all DPSs form of threat control, now I like to watch the other DPS's threat bar and try to make sure I'm higher on the hate list than they are, which directly translates to me having done more damage than they have.
3) Yes and no. At level cap (or 60+ at least), most jobs generally have enough buttons to hit to keep things interesting. Also, the duties get harder, so you're juggling more buttons to push with more things to avoid. However, at low levels (like pre-50, though some jobs really don't feel great until 60+), that answer is a resounding NO! Shadowbringers gutted a whole lot of superfluous skills, and streamlined others. At high levels, this was beneficial to reduce button bloat, but it sure made doing low-leveled content feel like a chore. Also, thanks to power creep, people can just kill stuff a lot faster than they used to, so some of the older content just isn't as interesting anymore.