Just tested them. In scenario when they ambush a single squad of unvetted shocktroopers (since they are most "fat" inf in the game), using STG+focus fire ability. They are able to put down like 3-4 models, before shocks came to close range and kill them almost instantly.
There are 2 problems here:
1- Ambush ability (same with paras) gives a debuff of .5 into receive accuracy. This is a huge buff to SMG like weapons.
2- Shocktroops have armor instead of RA. Unless they have vet or are crossing through cover, part of the buff goes to waste.