Interesting. I suppose you need to define "risk" in the first place.
(A) Is it the probability of a catastrophic collapse?
(B) Is it the probability of suffering a short (or medium, or long) term loss, however small.
(C) Is it volatility, roughly defined as rate of change of value?
If A, then equities are risky on an individual level, while incredibly safe when widely diversified.
If B, then both equities and property are less risky than cash! Particularly in the long term.
If C, then equities (subject to
@ronaldo point about day to day visibility) are riskier than property.
One further point. In comparing like with like, you need to count share price growth AND dividends against property appreciation AND rent roll.