SSDs are definitely not "cost-effective" for 10 TB if that's what you're suggesting.

It looks like HDD prices are at ~40% of SSD prices (new drives, not cloud-hosted). SSDs are starting to make sense for more things, now.

That comparison only holds for the smaller sizes.

For an 8 TB SSD and 18 TB HDD, it's more like 3x.

I mean to say, for general self-hosting services and apps, HDDs seem to have that performance problem and latency, which could lead to a negative experience?

Unless you need the performance. if you compare a single ssd to a raid 6 with 5+ drives to lower the seek times the ssd will always come on top