I'm not trying to argue but do you know the vet values of the royal engineers?
I do not think they have reduced received accuracy modifiers like IS/riflemen/conscripts
I only know they have increased repair at vet 2 and reduced reinforcement cost at vet 3.
I believe that hardly qualifies them as "toughest infantry".
Veterancy:
-30% cooldown WHEN IN COVER,+50% Reload WHEN IN COVER
Construction/Repair Rate increased by 30%
Reinforce cost reduced by 50%,received accuracy -33%
Size/RA: 0.8
Bonus while in light/heavy cover: 0.9
IIRC
+1 armor with upgrade (for reference shocks are 1.5)
With upgrades n in cover, toughest squad ingame.