Sure. Not really saying one is better than the other; SeaweedFS approach allows you flexibility with these decisions and offloading, GlusterFS has no dependencies on additional services to reach its full potential.
Currently using Minio which is a relative success. However as part of quality checks we're using a lot 'listObjectsV2' S3-calls to check for gaps in our data, which is pretty slow. When using SeadweedFS plus, say, a Filer meta-data store based on Redis, this would presumably be faster?
Of course you can go with faster filer stores. Default filer store would be enough for millions of files. It is the same speed as a common file listing.
Actually I do not understand why MinIO is slow here.
You can move metadata to any faster scalable data store. And/or move the data to any cheaper/faster/larger storage, in cloud or in your garage.