why are you reporting this here?
infantry health is quite obviously not realistic, because the spring engine has no way to make use of cover, or anything approaching realistic infantry behavior. if we used realistic infantry health, this game would be utterly absurd and there would be no point in using infantry for anything except capping flags after your vehicle army had swept everything clear.
their health just represents about the number of bullets that would have to be fired at them in order to bring them down - even 30 is probably too low in that regard, but it is better for gameplay if they die at some point.
as for cost, I don’t think you have thought about the implications for gameplay that such a change would bring. do you -really- want to see 3-4x more infantry on the field when most people’s computers struggle with the numbers we have currently? how would having dramatically more infantry who happened to die very easily improve gameplay? answer: it would not - you’d end up with much more WWI mass-rush kind of play, where the goal would be to build such a large army that in running them at the enemy you would have a large enough chunk survive that you could deal some damage before they were all slaughtered.
a unit being OP only when used by one player does not really qualify - there’s no way to tell if the unit is a problem based on its inherent ability/cost effectiveness, or because the player is outright better than other people at using it (which is almost certainly the case).
Please take more time to present your ideas more coherently when you next decide to post something like this. I value feedback of this sort, but you need to present it in a more thought-out manner, rather than just rambling through a list of things you don’t like at the moment.