If you want to pick a short term window of say, 2 or 3 years, and add in an isolated incident of a buyer with one property who loses money, then I'd agree with you.
But I'll guarantee that this was an operator error - not the vehicle of property as a whole.
We've experienced and benefited from something very similar to this. I'm sure it's pretty rare.
Our first PPoR had a checkered history. It was inhabited by a lovely elderly couple who improved it immensely and had a wonderful "street-best" garden. They eventually got too old to maintain the property to their standard and sold it to a young couple back in 1994 for 108K.
The young couple proceeded to fight and argue and bicker, and totally neglected both the house and the garden, to the point where it had "good bones" and nothing else. Barren garden front and back, a veritable tip inside and a warzone everywhere else.
Mr and Mrs Muggins (us) came along 4 years later when they wanted it sold before they killed each other. We started offering 79K, even though it was advertised as 'offers between 105 and 115K'. Even though they were fighting enormously, they managed to come together to resist us enough to make us come up quite a bit.
We eventually bought it in 1998 for 96K. A drop of 12K, or 11% over 4 years. Ouch for them. Yippee for us.
We still own it and rent it out to a nice young couple. It's back to looking good and worth 550K now. I guess we managed to pick up all of their growth whilst they systematically destroyed the cosmetics of the property during their tenure.
If you graphed it's growth over the years, there was a definite dip under their stewardship, but it was temporary and artificial. As soon as you put a little bit of TLC into it, it was back to tracking normally again after a little spurt. Gotta love those spurts when you are driving the train.
108K in 1994 to 550K in 2009 = 11.5% p.a. compounded (What the property has done overall).
108K in 1994 to 96K in 1998 = minus 3.0% p.a. compounded (What the fighters received)
96K in 1998 to 550K in 2009 = 17.2% p.a. compounded (What the property has done with us).