Why would Chromium based browsers be bad for competitiveness ?

Hey guys,

During my journey in the Linux sphere I stumbled upon a lot of content, especially Youtube videos that promote the use of Firefox to counter the rise of Chromium based browsers.

I completely understand that using another browser than Google Chrome is important to avoid a browser monopoly but I don't really understand the war that many Linux/FOSS enthusiasts leads against Chromium based browsers.

I don't see Blink (Chromium) as a competitor to Gecko (Firefox) but more as a successor. Gecko is old (even if heavily maintained) and is slower than Blink in many ways (it is perceptible to the end user and benchmarks proves it).

Blink is like Gecko an open source project and even if Google is at the lead of the project they can't really do anything that goes against the interests of the users or developers without suffering from a huge backlash. And even if they try to put their interests first there will always be communities to fork the project and remove Google's shit (ungoogled-chromium is an already existing example). And I am nearly sure that there will be in the future someone or a company to fork Blink and create a new engine, putting Blink at the same place where Gecko is currently.

For me the main reason to stop using Gecko based browsers is for compatibility, if all browsers end up sharing the same foundations, thanks to Blink, creating a website would be a much easier process and it might save time (and mental sanity) to a lot of developers all around the world while not compromising on privacy for the end user.

I am completely conscious that I might be wrong as a lot of more grown people from the community don't share my opinion but usually the explanations are limited to "do this to avoid a monopoly" so I wanted at least some reasons for this "war" against Blink/Chromium.