Are you high on drugs or sth? So the first guy wins the lane while the 3rd guy is sitting idly? 4v4 is fine. If you are into spamfests and memes. It's fine. Played 3 4v4 games in my lifetime (not counting vs AI I played at start), all 3 were horrible.
I mean, just look at Skippy's videos. Enough said.
First guy makes the pushes and takes the infantry engagements to start the game
Second guy moves his Machine Guns and At Guns around to provide support for the main line/vehicle guy and protect the flanks.
Third guy builds Ultra Lights and Lights to stretch the map early on, cap points (if applicable), carry infantry, and eventually becomes the star in the late game when armor becomes the defacto decider of who wins.
Fourth guy builds Mines, Sandbags, Wire, calls down artillery (can give him the mortar team too), builds emplacements and repairs vehicles.
Everyone has an important role to the team and everyone can work with everyone else to provide dynamic teamwork
(Mainline guy needs MG's to stop blobs, Vehicle guy to inflict bleed and flank, and support guy to provide cover and indirect)
(Team Weapon guy needs Mainline guy to provide a frontline, vehicle guy to clean up AT damage, and support guy to deal with opposing indirect which is his weakness.)
(Vehicle guy needs mainline guy to stop infantry from running down and snaring his vehicles, team weapon guy to both suppress infantry and provide alpha damage to other vehicles, and the engineer to repair his vehicles)
(While Engineer guy needs mainline guy to provide an infantry buffer, team weapon guy to prevent rushdowns, and vehicle guy for scouting to provide vision so he can properly support.)
All seems reasonable to me. Throw in some unique role related doctrines that provide you with a choice of resources based on which doctrine you pick and I think it'd be pretty fun.