The problem with EVERY game of this sort (i.e. Age of War) is, that playing defensively - which normally is a good tactic is total bullocks. If you don't get your units butchered you don't get as much XP - the whole game is anti-intuitive and therefore very hard in the beginning. Due to the population cap it doesn't help you to build 5 different units, in fact the opposite is true. The point that you lose everything on evolving and repetitive scrolling to the enemy base hurts the game experience too. So don't be so close-minded to say it's easy, because it isn't. It is, if you use simple tricks (2 units + water, no turrets) - but noone would use them in the situations you face, meaning:
a) oh god, the enemy seems to have more units than me - let's build fewer buildings!
b) their turrets destroy everything and the break through my troops - let's NOT build turrets
That's why this game isn't anywhere near good. The good tactics are illogical, there is only one map, one enemy, meaning the only thing you can come up with to make it interesting ist to try to get faster and faster. As I said before, there is no real difference between the difficulty modes, so it's always the same. But if you can't make it just look at the advices in this thread, because they work (I don't talk about the pro tips to get under 7mins^^).
Secondly: people who exploit the tutorial-"bug": you aren't good because of your ability to exploit.
Thirdly: Spawn rate upgrades work just well and are the most important upgrade for every unit.