A Mozilla dependent on Google seeing value in Firefox sending searches their way is at minimum as good as one in which Mozilla doesn't exist and everybody uses Chromium-based browsers, by definition - and in practice, way better.
But yes, more non-Blink engines in use in general would also be a better world. Alas, that, too, isn't the world we live in.
Same for translations btw, Firefox didn't have built-in translations for a while because Mozilla had to painstakingly work on a research project to figure out how to do translation locally, on your machine, without sharing the page you're looking at with an external server.
Spell-check doesn't send things to a server in Firefox - that's Chrome (and only with a particular setting, IIRC).
I'll emphasise that the "handful of concessions" are concessions to usability, not to having to share data with Google or DuckDuckGo. Firefox is still an incredibly private browser, especially if you consider the rest of the landscape.
But also keep in mind that it couldn't exist without Firefox/Mozilla existing. A world in which more people use Firefox over Chromium-based browsers is a better world.
Use Tor Browser if you want it dialed up to eleven. You'll quickly find that it's way more of a hassle to use, and also still pretty easy to accidentally compromise the security measures.
Of course Firefox isn't perfect; nothing is. But a 180 turn implies it's the opposite of perfect now, and it really isn't - especially in a world where basically every other browser is waaaay closer to that.
You said you knew there weren't going to be compromised certificates because there was a government website. But also notice that the kerfuffle is about
New legislative articles, introduced in recent closed-door meetings and not yet public
In other words, these are new additions that are not yet reflected in public documents. This article is also a good explainer.
Specifically, everyone who's not using Chrome and its derivates did it. Use Firefox, people.
By that, I know it’s not behind closed doors or undisclosed, nor requiring compromised certificates.
I don't know how you reached that second conclusion from the fact that there's a government website, but as https://last-chance-for-eidas.org/ mentions, it was hidden in plain sight, in that eIDAS wasn't hidden, but the specific consequences were:
Although the deal itself was publicly announced in late June, the announcement doesn’t even mention website certificates, let alone these new provisions. This has made it extremely difficult for civil society, academics and the general public to scrutinize or even be aware of the laws their representatives have signed off on in private meetings.
It sounds like you made up your mind in advance to support this. Mozilla (and I believe Google too) have a public and rigorous process to determine which certificates to include in their browser, and, importantly, which not too. This new regulation would enable governments to circumvent that process and force browsers to include their certificates, even if those are used to spy on citizens, or are insecure - like the government of Kazakhstan tried to do before. All this using a process without checks and balances.
Also note that parties like Google aren't trusted "exclusively" - you can always switch browsers if you don't trust them. That will no longer be possible with this regulation.
eIDAS has been through the trilogues unfortunately, so the Commission, Council and Parliament have reached agreement about it, pending final approval.
Wat goed nieuws mag ook wel eens :)