So nonzero variance is a sufficient condition for "gambling"
In that case, there's not a single moment in anyone's life when they're not gambling. By this definition, the term is useless; it provides no information.
If, on the other hand, we take "gambling" to include all its connotations in society, then APs are certainly not gamblers. Gambling connotes an activity where the excitement comes from chance alone, without regard to the EV, and in fact, usually despite the EV which is almost always connoted to be negative. Gambling as society understands it is expensive at best and ruinous at worst. Clearly none of this applies to AP. To put it another way, the variance is what makes "gambling" fun and the EV is what makes it undesirable. For advantage play, precisely the opposite is true!