There were only tests of vet 0 Ass-Grens vs vet 0 Assault Sections.
No tests of vetted 6 man Ass-Grens vs vetted Thompson Assault Sections.
Well given that UKF design they do not actually have to be better than "assault grenadier", I am not sure why they lose since their stat are comparable and should be about equal fight might had been RNG or test parameters.
Actually I use the doctrine allot in 2vs2 and it already quite good, one should be careful with buffing them.