HDB certainly helps to lower the barrier to entry in home ownership. But I don't think most forms of HDB purchases are investment-orientated. ROI for second-hand HDB is not high and buying a good first-hand one is like winning a lucky draw.
I would say HDB is more of the gov's mean to stabilize the housing market and it functions as more like the backbone of the economy. (Or you end up with runaway prices like in Hong Kong.)