Hello @rodrigosato (and whoever else feels this topic addresses them):
There is indeed a point at which you cannot continue to play for free. This point is reached after about 30 hours of Gameplay if you are really (really) good and are used to the system.
Funny enough, there is also a point where you cannot continue to play for pay. That is simply because there are no more levels.
After having established this, the actual free content becomes more and more each week. New levels are developed by the Owners of CodeCombat as well as the community and published for you to play. There are currently four worlds filled with free levels and after having completed them you learned more that just "a little". Before calling something "Bad marketing strategy" you should notice that you got this all for 0€ (or $, ¥ or whatever you use to pay). I could understand if you call them silly because they basically give it to you for free, but that is your personal opinion. Their model works, as shown not only by this game but by many others as well. Free-to-play is an established business-model after all.
Your rant sounds more like you are stuck at a level and can't buy the best equipment to solve it by brute force. But sometimes you have to work with sub-optimal tools. What you don't have in lifepoints try to think of a way to take less damage. If you face too many enemies at once try to find a way to fight them after each and not all at the same time.
But most important: Think before you buy! You have a limited amount of Gems and you should not waste them. This is just like in the real world. Do you really need the new helmet, or would a new sword make more sense. Do you buy the medium helmet now, or the better helmet later?
Wasting resources is your personal problem.
If you are stuck on a level this forum is the right place to ask. But be aware that we usually do not hand out complete solutions. You can ask how to solve a problem and you will (very likely) receive an answer. But making a game bad without even trying is just bad style.