I don't know when you tried this, but I don't think this is valid anymore:
1. If cold start times are a big deal, you can now set a minimum number of instances with Cloud Functions so they don't scale to 0. You can also now set concurrency on Cloud Functions so one function can run multiple requests simultaneously on a single function.
2. There are tons of other serverless options if you want to, say, have a Firebase front end but a backend API served in your language of choice that uses the Firebase Admin API to do whatever you want, e.g. App Engine or Cloud Run.
1. If cold start times are a big deal, you can now set a minimum number of instances with Cloud Functions so they don't scale to 0. You can also now set concurrency on Cloud Functions so one function can run multiple requests simultaneously on a single function.
2. There are tons of other serverless options if you want to, say, have a Firebase front end but a backend API served in your language of choice that uses the Firebase Admin API to do whatever you want, e.g. App Engine or Cloud Run.