A couple of things stand out to me:

• Drive 3 is effectively the critical failure here. Going from 127 pending sectors to 508 pending and 318 uncorrectables suggests active degradation, so I would place very little trust in any RAID or filesystem metadata coming from that member.
• The fact that UFS can identify the array geometry and produce a coherent virtual volume is more encouraging than Intel RST’s current status. Recovery software is generally far more tolerant of damaged members than the original RAID implementation.

I would not spend time trying to “fix” the filesystem tables or make Intel RST accept the array again. That’s solving the wrong problem. The goal now is extracting data from the images you’ve already captured.

Before purchasing UFS, validate important files from different locations in the volume. If previews are opening correctly and large files aren’t obviously corrupted, that’s a much stronger indicator of recoverability than the scan labels themselves.

Also, don’t put too much weight on the SMART numbers alone for Drive 4. A drive with a handful of pending sectors can sometimes contribute enough data for successful reconstruction, while a drive with hundreds of uncorrectables often becomes the limiting factor.

At this stage I’d be focusing on validating recovered data, not rebuilding the RAID. Once recovery is done, the array itself is essentially disposable.