Well, it's a guarantee that this change will give Chromium a higher market share on iOS, since the current market share of Chromium on iOS is exactly 0%.
How much of an effect it will have remains to be seen. But Google has shown themselves quite good at overcoming the default browser advantage by making other browsers not work well on Google websites and by pushing pop-ups into people's faces telling them to "upgrade" their browser to Chrome.
> Well, it's a guarantee that this change will give Chromium a higher market share on iOS, since the current market share of Chromium on iOS is exactly 0%.
Yes. Both the real browser engines in Chromium and Firefox are starting from absolute zero on iOS, and Chrome will certainly be much higher than Firefox.
But regarding ios, at this point this is just speculation. Safari has the "default browser" advantage and people are used to it.