I agree in principle, but to use the grid system as an example, a character that's "adjacent" to another creature can actually be between 0 and 10 feet away from them, as they both occupy 5 cubic feet volume (I guess technically they could be even further if one can fly). 10 feet is definitely enough to be able to fire, and you can always manage at least 5 feet, which is a bit more questionable, but not impossible (I'd say... maybe disadvantage?
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