I think mbtiles are being phased out for pmtiles because no DB required and can be served from static storage like R2/S3 (with a worker but hopefully the worker part goes away and they support byte offset requests soon)
You don't need a database to serve mbtiles. If you're deploying PMTiles somewhere that doesn't support byte offset requests, then they don't really have much advantage over mbtiles.
That depends what you mean by needing a database. MBtiles files are SQLite database files, so you need a SQLite process running somewhere to extract the requested tiles.
Look at the network tab on https://pmtiles.io/#url=https%3A%2F%2Fdemo-bucket.protomaps....