As an oversimplified example:
If a website has 100 visitors, and 99 of them use Chrome, and 1 user uses Firefox, it doesn't matter how good their fingerprinting resistance is, they're always the one using Firefox.
If a website has 100 visitors, and 99 of them use Chrome, and 1 user uses Firefox, it doesn't matter how good their fingerprinting resistance is, they're always the one using Firefox.
[0] https://radar.cloudflare.com/reports/browser-market-share-20...
However, if you're trying to search for somebody, and you're able to eliminate 96% of the data, you're in a much better position to accomplish your goal.
Whether or not you should care about this depends on what kind of tracking threats you're trying to avoid.
Even if every Firefox browser gave off the exact same fingerprint, that wouldn't make the network traffic indistinguishable between Firefox users. There is a lot of entropy that is provided by your network stack of your device, the networks you connect to in order to get to the end website, the behavior of your requests, etc.
Now, most websites aren't doing this kind of analysis. But it isn't unheard of or impossible. There are major websites that are known to do TLS fingerprinting.