RAID vs software defined Block Storage

As far as I understand was RAID invented to protect from hardware failure induced data loss:

• Say, you have 2 harddrives in RAID1, one goes south, lucky you, the other one got your data.

• Say you want better storage capacity than RAID1 and have no special requirements for write access, there is RAID5 waiting. One Disk goes bust. Lucky you swap it out, wait until reconstruction is done. Everything is fine

On the other hand there is software defined Block Storage which abstracts from nitty gritty details of hardware. In principle does it something quite similar: Storing information redundant across several physical drives.

In which scenarios are RAID-Solutions still the way to go?

to protect from hardware failure induced data loss:

No. RAID is intended to reduce downtime, not data loss. For data loss protection you are supposed to keep backups.

On the other hand there is Block Storage which abstracts from nitty gritty details of hardware. In principle does it something quite similar:

No. Block storage - the term in itself - makes no guarantees about redundancy. Many block storage devices can implement redundancy, but it is up to the user to do it and not necessarily required.

In which scenarios are RAID-Solutions still the way to go?

This is a VERY good question. Less and less, I would assume. Generally RAID gave better possibly performance due to hardware write back caching. That said, today I build a distributed (multiple computer) block storage with terabytes of fast SSD write cache based on a 2x100 gigabit crosslink from every server - there is no RAID card on the market that can keep up with that, including uptime (because my RAID 1 actually is mirrored on servers).

I would say the air for RAID hardware is getting thin.

Btw., RAID 5 you can pretty much forget for large discs - anything above 2TB is too risky, RAID 6 will cover you for a little more space but it tops out too. Further reading - https://www.zdnet.com/article/has-raid5-stopped-working/

Hardware (i.e. self-managed) RAID are usable, when:

1. the physical maintenance is about to be done by some less-qualified "remote hands" staff. "Pull the drive with LED blinking and replace with the new one please".
2. the hardware itself might contain additional safeguards, like battery to ensure the buffers are actually written to the disks after the system is rapidly powered down.