@derp
It's like the loose leash walking has made him calmer and he has gained more self control.
Absolutely. Impulse control is a major component of reactivity. Think about it in terms of something like road rage; the people with impulse control aren't the ones losing their minds, flipping people off and being a general menace out there.
The more a dog pulls, the more tension is being created, and they're being rewarded for that tension inadvertently, most likely, thereby creating kind of a feedback loop situation. If there is constant tension on the leash, you're also conditioning the dog to the collar being tight around their neck, which means over time your dog will care less and less about pulling.
It's hard to say for sure over a post on reddit, but if you're dog is reacting that means they're over their threshold. If your dog is
under threshold, they won't notice whatever the distraction is, and conditioning is pointless. If they're
over threshold, they won't focus on anything
but the distraction, and conditioning is hopeless.
The goal is to find your dogs sweet spot where they notice the distraction, but you're still able to redirect them back to you and rewarding with whatever method you choose for ignoring the distraction. If you aren't able to set up a controlled environment with a trainer, the next best thing is finding somewhere populated with whatever triggers your dog that allows you to maintain the spacing you need to work them. As your dog's impulse control improves, you start to close the distance on whatever the distraction is, finding the new sweet spot.
Whether you use food, or toys, or attention as a reward is pretty irrelevant, as long as your dog values it. There are a few things you can do to increase the value of whatever reward you choose, but it depends on what that is.
A gentle leader isn't going to help with any of that. If you really wanted to go with the corrective collar approach, a prong is a hundred times better because it allows you to communicate much more effectively what you want from your dog. Like any tool though, it can be counter-productive if not used properly.