Deadlift not progressing because lower back keeps on rounded and squats catching up!

[Mugaaz]

There is no "truest display of strength". There's a bunch of ways to display strength. Everyone has a fetish for their favorite/best lift. That doesn't make them the one true scotsman.

[jbackos]

You are not loading your hamstrings before the bar leaves the floor. You need to bring the chest out "proud chest", squeeze the upper arms backwards with the lats "protect the ribs", and feel a lot of tension in the hamstrings. The hamstrings anchor the pelvis so that the glutes can work their magic.

I also suspect that your abdominals are very weak or your haven't learned to brace. Get a belt and learn how to use it. There is no moral superiority in lifting heavy weight beltless, despite what the "raw nazis" would have you believe.