This would give me a more constant exposure to the wins and losses and reduce the luck aspect we now see in investing. Another benefit is that the max profit would stay more constant than now.
I'm not sure about that. I think if it became popular for people to use the feature, it would cause bigger swings in the max profit. Whenever any new investment came in, lots of existing investors would automatically increase their investment to keep the same percentage, magnifying the effect on max profit of the new investment. And conversely, and divestment would immediately be followed by a bunch of automatic divestment by people aiming to keep the same percentage of the now smaller bankroll.
Also, does it make any sense to want to be a certain percentage of the bankroll? I don't really see how it does. You're risking up to 0.5% of your investment each roll no matter how many others are invested.