It means that Google can push technologies that benefit their ad tracking business, or choose to use non-standard APIs to make their apps run faster than competitors. Both of these things they're already doing. While they might not go the route of Microsoft, putting their Active-X plugins in IE, using deprecated and non-standard APIs is pretty damn close.

Furthermore, all these forks result in bugfixes and new features making it back into Chromium. That allows Chromium to evolve faster than other browsers. That's not to say that Firefox hasn't been keeping up and pushing past Chrome on some important fronts (CSS Sub-Grid, for one), but I'm afraid a point will come where Firefox can't keep up with all the new web APIs that developers will want to use.

Another fork of Chromium doesn't lessen Google's influence over the market.