Low 30's (33%-ish) is not good, borderline bad, but doesn't suck.
Hypothetically, assuming you can only shoot one or the other, a 33% 3pt shooter is equally as valuable as a player who drops 50% of his 2-pointers. Since only about half of the qualifying PF's even average 50% shooting inside the arc and SF's who do is reserved for the elite, I'd say 33% is not awful. Yes, we all know sports do not exist in a vacuum, and comparatively, 33% would not put him in in great standing among SG's; however, 33% is the benchmark for whether or not it's worth it for you to shoot 3 pointers. If it's justified that you shoot them (33% is justified), then you can't 'suck' at shooting them.