Innogames wants the best from us... and this is our money.
Without an upgrade your progress is slower, but you can get the same as a premium player. A little example: I am a premium player and I can produce more goods than my neighbors, but more is not always better. I have 38k marble, 24k steel, 43k planks and usually 4.4 million coins in my storage. This is a lot, but it make no difference to have 2.000 of each good, because I have no possibility to use it wisely. Other example: I have thousands of thousands military units, but it make no sense to use it... if I fight one NPC enemy squad can kill alone my hole army. It make no difference if you have 1 unit or thousands, the result is the same. --> you will loose
Have a look to the game progess, for me ends the game in some months, because I have than all what is possible in the game. Without premium you can play longer, this is an advantage.