As for difficulty slider, you really shouldn’t see much red for missions (bosses only, and even then pretty sparingly) on the standard difficulty and if you are, it’s likely a bug.
As for AV you can solo all the way thru and never see one unless you are soloing TF. In fact, I’d argue that the way the game is supposed to be designed, no one should be able to solo an AV (I know it can be done, but it’s nothing any player should have to worry about).
And I get that there are some yellow/oranges there, but again, game design shouldn’t put the player in positions where the best they can hope for is a yellow to show up and that no red or purples pop up around the corner.
So the question isn’t is it doable, but rather is it appropriate for the level to solo. Now I will say that same design still needs to provide some challenge for entire level range of that contact, so for a lvl 10-15 you should ideally have lvl 10 minions and lvl 15 bosses (which would be deep purple to a lvl 10), but more on the lower side and less on the higher side.
Sounds like from RikOz’s experience that’s not the case?