I would guess that you are right that stagnation would result with big companies keep taking money, while smaller investor or just regular people not growing with it, so all the big companies would take all the money. But when we are talking about stagnation, we should not just take it face value, we can't just say this is why it is bad, we should compare it to make sure that it is bad.
So, when you compare stagnation to inflation, which one seems worse to you? I would say a very very high inflation could be much worse, of course a 5% inflation would be fine, that is not too much, I think people can live with that, anything under is perfect, but what if you had like those famous 100%+ ones? Argentina had one, Zimbabwe certainly had a lot more, and Türkiye recently had one I believe. Those are much worse than stagnation.
When stagnation happens then the whole sector gets worse and the ones who benefit are the ones who have the big capabilities like the companies. Meanwhile, economic growth in the lower middle class will be hit so hard and they will even have to close all businesses that have been built for a long time. I don't look far because that happened when Covid hit and hundreds of small and medium businesses had to close all their businesses because they could from the stagnation of economic growth.
Both are much worse because they have the same role in killing economic growth. Like some of the countries you mentioned and maybe even many more who feel the impact of all that. The broader solution is that the government must have a way to overcome it and each individual also tries to prevent inflation so that it can be restored simultaneously.