I don't see how this is paranoia.
I wouldn't use the same password for my phone and my banking acount. But the fact you can't change your fingerprints pretty much forces you to.
Worse, you will use the same print in the future, forever.
So how long is that password going to last, with all the regular leaks, phone-malware and whatnot? How many years?
If any single application you gave the fingerprint to has a security hole, just one of them, then all other are immedeately compromised. And there is no way you can change that, even if you knew it happened.
And the best part is, because the 'password' is so strongly linked to your person, everyone who got it can easily figure out which other locks it might open for them, other than your phone.
Lastly, the argument of 'the xyz could do it if they really wanted' is just a bad one and I'm sick of hearing it.
This is still a question of economics.
Sure there could be agents following everyone around, grabbing fingerprints from the used glasses in restaurants and so on... would only cost like a trillion dollars until we have all the data.
Or we have them all upload their prints to their phones, which we already have backdoors into anyway, so it costs one of our IT people 10 minutes to issue the download command.
One thing will never happen, the other is more than likely.