[…] correcting or adding constraints to fully constraint the drawing is a wild goose chase.

I’m not sure I understand what you mean by this. Could you elaborate?

[…] navigating which part of a line (and which line) is selected […] is a wild goose chase.

Do you mean if they’re colinear?

[…] Let’s say that you have two lines in a 90 degree corner. If you add a line in the middle of any of the two lines, the cursor shows you that it will add a coincident constraint. But when you create your line, the coincident constraint isn’t applied. […]

What you’re describing sounds more like a bug to me. At any rate, I wasn’t able to confirm the behavior you described (maybe I’m misunderstanding you?):

^[1]

I was able to get both a symmetric constraint (green arrow), and a coincident constraint (red arrow) on the two 90 degree lines.

Maybe I’m misunderstanding you, but FreeCAD tells you when a constraint is redundant, and clicking on it highlights the respective constraint in the sketch:

^[1]

Could you be more specific?

[…] FreeCAD is trash […]

What issues have you had? What features do you wish it had?