What other similarly sized or smaller company has successfully built a browser which is not Chromium-based fit for the average consumer? If you're just piggybacking on Google's work, then sure, it's probably not bad, but Mozilla has their own browser engine and is trying to keep feature parity with browsers which have effectively unlimited funding.
This Google-controlled narrative is pushed out onto a lot of things (i.e search) which people are slowly starting to realise isn't that complex or expensive to build after all (see Brave Search for example). It's not surprising that Mozilla would echo similar sentiments considering the entire company is controlled opposition.