I’m very junior, so take what I say with a grain of salt. But when I was determining if I should use Firebase or not, my biggest hesitation was simply that if Firebase ended today, I have to completely transition my application’s architecture.
Though that is unrealistic, even thinking about it was enough to make me want to be in full control of my application’s various layers.
You are bringing a senior consideration to the table; they can and do change their pricing at any time for any reason. Also, every single day you rely on them is a day that your architecture grows on that volatile cornerstone. Would look at https://parseplatform.org/ or https://postgrest.org/ as alternatives; turnkey, hosted solutions are available for each.
This is not a junior consideration and it's not unrealistic that firebase ends in say, the next 60 days which in terms of porting your entire application is essentially today. You're right to weigh this as a concern in evaluating approaches and everyone should, regardless of experience.
All PaaS providers work hard to couple you to their platform not (necessarily) for nefarious reasons, but because that's how abstractions work. You need to be continuously vigilant and aware of when and how you are tied, do a cost/benefit analysis and have risk mitigations for things like your original thought, so good for you.
Though that is unrealistic, even thinking about it was enough to make me want to be in full control of my application’s various layers.