Doubts about system portfolios.

Here I feel that among the systemists there is an opinion that a portfolio of systems for one or related instruments will smooth out drawdowns and give more even profit, that is, it will turn out smoothly growing schedule. Although I use many systems myself, but from a non-mathematics point of view, and life experience there are doubts about this. Well, yes, on history, you can mathematically select a set of such systems, which will smooth out the total drawdown and smooth out the total equity as much as possible. But history rarely repeats itself, and in the next instant after testing, a new countdown will already start with completely different optimal parameters.. Where it used to be smoothed, can, on the contrary, increase the failure, where was the growth, there may be a fall and other manifestations of an efficient market.
Here is for comparison, for example, which equity will be smoother — first option, if we play toss with only one opponent, or, second option, at the same time with ten? To my mind, chance will act here.
That is, it is impossible to predict which equity will be smoother. — on the portfolio of systems, or on one system. Although I want to believe the opposite, because, remind, that I play a portfolio of systems myself.
Someone will say — this is how opposite systems should be played, for example, trend and counter-trend. Yes, in this case, really, in theory, drawdowns of one system should be smoothed by another system. But there is one catch — for example, on futures, only trend systems work and merge counter-trend. I will immediately insert two caveats — we are talking about American futures and stocks not lower than daily(I don't know about the Russians) and about my personal experience in systems building (maybe someone came up with a counter-trend system for futures, but not me). And on stocks and stock indices, vice versa, counter-trend systems work and merge trend. So that, the result of combining trend and counter-trend systems into a common portfolio for trading related assets will bring zero result.
I repeat, these are not statements, but only my doubts, since I don't know the answer to this question. This doubt is based on real life experience of gambling., but not theoretical mathematics, since my knowledge in mathematics is limited to the elementary operations of multiplication and subtraction :)