You are not wrong, bonds in general but especially long duration have gotten crushed. Facts are facts but cherry picking the high to the low is another thing too. You somewhat referenced it but you could just as easily have said if you bought bonds in 1980 at 16% you would have made a killing on interest alone and another killing on principal appreciation. That's why there were bond kings back then. <snip>
I used those dates contrasting 2020 to the early 1980 to illustrates that when talking about any asset the context matters.. There's a time and place for ovrweight exposure to anything when the conditions are right, and a time for under (or no exposure) when the conditions are the opposite.. just hiding behind averages doesn't tell us anything and, worse, can get you killed if you cannot survive the barren periods - quoting Howard Marks, never forget the the 6ft man who drowned crossing the river that was 5ft deep - on average.
I think there are times when things are way over done in one direction or another and its obvious as can be but for many either fear/negativity or greed/optimism win out and either keep people out of or in the investment for too long.
I think the middle 80% or the range is far more difficult to ascertain. Right now for instance, are bonds bottoming or half more room to fall or will they rally - as said above yields are in line with historical averages so that better than the extreme but as you say if yields go to 8% then bonds get crushed but if they go back to 2-3% they rally and do well. IDK.
Personally, I when covid hit and rates went to zero across all durations I moved almost all of my bond AA to cash or ultra short duration (and some into equities). Even now I am mostly money market or short duration but over last year and half have moved bits to BND (intermediate duration) any time the 10 year UST has crossed 4.5%. I am probably up to about 10% of my AA in BND now and basically at yields where they are today (so no gains). If I was smart and a trader I would have sold when rates when down.
Don't know if it will be good or bad but really my overall duration mix of my cash/bonds is probably around 2 years so clearly I don't have high conviction of what direction rates will go.
I think as long as governments keep buying/hoarding gold and the trade nonsense I don't see how yields go down materially unless there are obvious signs of a recession. The deficit is another problem but that is the tail wagging the dog of gold and trade.