Therefore a Safety Pilot needs to be qualified to act as PIC in the aircraft under all expected flight conditions
Indeed.
I was once test flying a C 172 with a mod installed. The "Chief Pilot" wanted to come along, so I let him that flight. During the course of the flight we chatted. I learned that neither he, nor his other pilots had flown in the last six months. He was planning to check them all out the following week. When my flight test was done, I said: "Hey, perhaps you should fly a few circuits from the right side, so you're fresh for next week, as I'm here right now anyway.". He agreed.
His first two attempts to land were bad, and I had to "help" to prevent damage. His third would have resulting in damage for sure, other than I took over with an "I've got it". This pilot might have been "qualified" to fly right seat, but he sure was not
"qualified". He could not even land himself, much less possibly fix someone elses messed up landing.
Generally, I view the role of "safety pilot" with caution. I'm worried that there are pilots out there doing this, even for another pilot who's just not current, and the sum of "qualification" in the cockpit is still a bit below what would be ideal.
If the regulators spent more time writing clear, unambiguous parameters within which a licensee should act, and less time on labarynthine a55-covering"gotchas" , -we wouldn't have a load of professionaly qualified people arguing about the regulations within which they are supposed to aviate.
But give 'em a break. They are writing the "last word" - the one which will be dissected to death by the lawyers later. They have to assure the intent is fully conveyed. And then, the justice department will review the proposed wording, before it becomes a reg. If they cannot figure out how they would apply it in court later, it is rejected. I spent a plot of time participating in working groups for regulatory change, and was very pleased with the care and precision I saw being applied to regulatory development.