Don't know about everyone else but I really struggle to face off against MGs as brits.
What you mentioned is a major downside of brits, having no opening alternatives but I think an even bigger issue is the lack of indirect outside of mortar pit.
No non-doctrinal mortar or rocket arty and even then the doctrinal rocket arty a literal glass cannon that takes forever to aim and reposition.
Brit design also factor in emplacements as 'units' instead of optional buildings.
Every faction has 4 buildings/upgrades with 3 units per building/upgrade. Brits have 3 buildings/upgrades with 3 units per upgrade. The 3(4) emplacements make up the other 3 units that they miss. Because emplacements are easily counterable, they become a somewhat predictable and underpowered faction compared to all the other factions. The recent Brit buffs was a move in the right direction but only a bandaid fix to the real problem.
(I do ignore the fact that late-game brits have unit modifiers to 'add' variety but that is an argument for a different thread)
I think a lot of Brit doctrinal units should be moved to non-doctrinal and some abilities put in to replace them. Similar to how the IS smoke and Assault Officer was added to fill in a niche that Brits lacked. Units like mortar squad, land mattress (buffed though since the current one sucks), assault tommies and tank hunter infantry.
