By definition, they are gravity wells proportional to the quantity of stuff they can offer. Smaller gravity wells are disproportionately easier to escape from, granted, but I'm not so sure the ROI of random asteroids will make up for that.
The commenter you replied to likely understood this, so it seems superfluous to point out.
Even visiting the ISS is a form of "going down a gravity well." If every sentence must be accompanied with an asterisk and a "well, actually" explanation, nothing of value ever gets said.
Consider Halley's Comet, which has a volume of approx 960km^3 and a mass of 2.2×10^14 kg. An astronaut standing on the surface could reach escape velocity with a not-all-that-robust vertical jump. For similarly sized celestial objects, the real trick might be not escaping their gravity well.
Granted, it is technically correct to point out the difference is merely quantitative. However, the effects of that merely quantitative difference are so pronounced that in any practical sense there is a qualitative difference in how we would interact with such an object.
>> Even visiting the ISS is a form of "going down a gravity well."
That's my point, though. If they're negligible as gravity wells, what's the point over just a space station? Working isn't any easier. We can't choose its location and orbit so easily. Resources to extract aren't significant. What else?
Of course you are. Gravity wells are where the stuff is.