The mining difficulty doesnt affect bitcoin inflation, so there is absolutely no point in having it increase, other than deliberately creating a centralized system, which is foolish
You want fixed cap/supply - you need adjustable difficulty
You want low difficulty forever - you have unlimited supply
And yes, Satoshi was aware of that.
There should be some other way to resolve that dilemma. Again i`m no technical expert, but I find it hard to believe that nobody in the world can come up with such solution.
Yet there are coins like Bytecoin that solve this issue.