You don’t need to modify the relo list (32) or smart (21), but you need to modify the g-list (34) to get rid of the reallocated sectors count. Clear it using VSC or rewrite it with an empty module, parameter 05 will be cleared, the write speed will become high again, and of course, all defects will return.
The reallocation event counter is located in module 21, in subsection 9 or 10. There is an edit21 utility to facilitate its editing. The module must be read from RAM, edited, returned back to RAM, and then the hard drive is given a command to write the module to the service area. Perhaps this number is written there several times, you just need to look with a hex editor where 2611 occurs (in hexadecimal form) and change it to zero. It happens that the value is not found in its raw form, but these are only a few of these parameters - they are reset by replacing subsections with empty ones. This counter doesn't affect anything at all, it's just statistical.
Could this be related to a firmware/SA issue (for example the relocation list or translator), or is it more likely to indicate a head/media problem?
Technically, this problem arose because due to the huge number of remapped sectors, the hard drive turned off the write cache (check with any available utility to see if it is actually turned off before doing anything), but the source of the problem is mechanical damage.
Such a hard drive can still be made to work and restored until you get tired of it, but I agree with the opinion above - I would not use such a hard drive for its intended purpose anymore. Except for a movie archive, where new files are occasionally written, old ones are never deleted.