I dont agree with you in many points.
In my opinion it is necessary too build units FAST to get middle (15% income). After they spawn you can tier up or go on gas.
I am not a fan of faster units. Units in a big group fight longer and much more efficient than units in smaller groups.
Dont worry about "fast" t3 units, they can easily be counted with t1/t2 units.
There are no phases in the game. It is always different what types of units will be spawn.
Just my experiences