y tru, no doubt it would work! but its all about timing and seizing initiative isn't it? Holding 2vs1 isn't easy...then again they might expect a flank attack at some point or they wont overextend, depends on different things from their part, its always a different adversary...
Thats why coordination is always key, & a little planning always makes a difference...my 2c...

Viper ur first comment what if u put a med army and all there army goes to do 2v1 and. Bring a large army in there flank cause they wouldn't see it coming would they

usually, one of us takes longer to deploy because its a bigger distance...that will attract more enemy attention because they will go 2vs1 to the closest enemy...they wont go where we are stronger, or have an advantage, that's for sure...

exactly, that where auftragstaktik, comes in!
But, i still believe we need general guidelines:
often we say: i go to G, u go to E...ok, but why??? jusy because its in front of us?? isnt there a better & faster & safer way to deploy somewhere else maybe???

i think we need plan in game,it changes when enemy movement changes,not depend on a plan before game

Also, thts why u need a plan!! To counter their moves before they do them imho (do u play 'go' at all??) to figure out (through experience/trial & error asw, ofc) the different places where they will come from, to confuse them/shift their attention elsewhere (especially on big maps) & more importantly, to coordinate our forces: I've seen time & time again it is the most effective strategy. That is why most people rush in pairs, they resupply/rearm each other twice as fast & keep the rush going.