I think this is not true anymore. We've seen many good players just not building the HMG42 early game and still being really effective.
All allied early game have been nerfed in different ways lately bringing more diversity. Mobile defense not being anymore a panic button shows how Ostheer compete really well early game.
Watch GCS2 Quali 1 Round 1: CreativeName vs Refero G2, Not building HMG42 and still a solid early game for the Ostheer player who will win the game.
Well I would say Grens are fine against Cons and beat tommies in most situations. Rifles though will likely require the mg42 as gren spam gets face rolled by rifles typically. \
IMO worst early game infantry is Tommies by a long shot. 280 horrendous movement accuracy, low rof outside cover and super inflexible.