They're modelled to have the same range. But there are several confounding factors that might make the experience with them seem like there is more or less gain.
- As others have mentioned, real pots that are used to control the knobs on real amps have variability. Sometime at 5/Noon the value is actually only 40%, or as high as 60%. Usually these pots start and end around the same places (0 and 10 values), but the area in the middle can be higher or lower than it should be, or than it is on another amp, because of this variability. The AF3 idealizes this, so all knobs behave how a perfect knob would, but not have a real knob you compare it to might.
- Master volume differences: Power amp saturation can add additional distortion. Comparing your Axe FX to a JCM 800 at bedroom levels, you might think the model has a lot more gain. But if that model has the Master Volume at 5 and the real amp has the Master at 1... the model is adding a lot of gain you'd only see when you turned the real amp up loud.
- Also related to master volume, on real amp often the volume only increases for the first 1/3 of the knobs travel, then the rest is just increasing power amp saturation. This makes it a bit harder to finely adjust, so on the AF3 the master knobs are all changed to have a more linear travel. So 5 on the Axe FX might only be 3 on a real amp, which can also cause there to appear to be differences in tone at the same settings, when really it's just the same knob reading, but not the same value.
- Sometimes people actually dial way more gain into their Axe FX sounds when they're dialing them at bedroom levels, because it doesn't sound as saturated as a real amp. But actually, once it's up to the same volume as a real amp they behave similarly, and the bedroom dialed tone might have way too much gain because of it.
- Others might think the Axe has less gain than a real amp because at loud volumes your real amp will be vibrating the strings on your guitar, causing a feedback loop that makes all your playing a little louder. You can do the same with a loud Axe FX, but if you're recreating tones at low volumes or with headphones you won't get that. The Gain Enhancer in the output section of the AMP block helps simulate this.
So I'd say they're supposed to have the same gain as real amps they're based on, but there's a lot of extra factors which might make it feel like the models have more or less depending on the exact situation/settings.