I think that is a very general comment. Depending on the car I would both agree and disagree with it. Take a Toyota Hybrid, that tech has been around for quite a long time and it well covered by lengthy warranty periods (and plenty of third party options if the batteries fail where regular battery inspections weren't done or on older models), therefore I would have no concerns there.
Taking a Nissan Leaf on the other hand, I would certainly agree with you.
As for Mercedes hybrid, you are getting a car with lots of depreciation so getting plenty for your money. Also as it is a hybrid and once the battery doesn't fail (there have been very few instances of battery failure afaik), battery degradation while frustrating is not going to be a big issue.
Having said that I would be cautious buying a Mercedes BEV given how relatively new Mercedes is to the technology.
As Paddywhack0 mentioned, used car prices have increased (and are still increasing here in Ireland) and are unlikely to drop significantly in the next couple of years given the overall lack of supply (with global chip shortage and the higher price of new cars etc).
Personally I never see a car as an investment (not the ones I buy anyway!!) as long term they are depreciating assets.
You are right that the evolution of tech is an issue, however, that has always been the case (safety tech, driver assistance tech etc) but you will have a very sizeable cohort of used car buyer that doesn't really care or really consider this. They buy cars on the cars merits and not what newer models can do. They are very different from people like us who post on motor forums!!
So once the car can do decent range (not limited to 50 miles BEV for example - older Leaf) or can be filled up at the pump to cover decent range without costing too much, then most used car buyers won't really care.
