Not really. That's basically saying that if those Pokemon weren't common, you'd be able to find Gible more often, which doesn't make sense. The sole reason Gible is hard to find is that it has a low encounter rate; it's not because the other Pokemon in the area have high encounter rates. There could be 50 different Pokemon in the area -- each extremely uncommon, or even more so than Gible -- but if Gible's encounter rate is set to that same low number, you would find it any easier. There'd be a wider range of possibilities for Pokemon you could find, but that wouldn't affect how often you could find Gible if its encounter rate remains the same.