I see what you mean and I agree that there is no right or wrong. It really depends on the person.
I think where we have a misunderstanding is in discussing tightness to explain poor mobility vs muscle recruitment. When referring to tight hip flexors because of poor mobility, most people are referring to limited range of motion where the hip flexors feel tight at the end range of motion. What I was referring to was getting them tight as in recruiting those muscles and keeping them tight throughout the range of motion so they remain under tension.
I don't agree that the hip flexors automatically get strengthened in the squat/deadlift because it really depends on a person's technique. It's common to see weak hip flexors be the cause of bad form, especially for beginners starting off.
All I'm trying to differentiate is mobility and strength. A person can have very mobile hip flexors that can be very weak or very strong, and the opposite can also be true. I'm just trying to prevent confusion since you talked about strengthening your hip flexors and saying that it is related to mobility issues but that is more of an individual thing.
Tight hip flexors (with respect to limited range of motion) inhibiting glute activation is directly related to mobility and not strength. It's definitely nice not to have to train hip flexors directly but some people can benefit from it.