I really wish they would change this as its pretty much the sole reason I don't play a lot more of Thresh. I mean I understand that the execute proc's on melee attacks only and that Thresh has more range on his AA's than most melees do, but that doesn't really make him a ranged champ imo. There's no projectile leaving him and flying towards someone and at the end of his attack his weapon is still in his hands. You wouldn't call someone with a long spear "ranged" just because they can poke someone from farther away than if they had a sword instead would you? Most games treat whips/chain weapons as melee weapons, and Thresh should fall into that imo.
Not to mention that his flay passive is designed in such a way to give you favorable trades by boosting the damage on your autos. Having to constantly blow that bonus damage on killing minions seems counter-intuitive to how his kit was intended to work. It's only gotten worse since the last change to relic shield (gives charges more often than before). And god forbid you try to blow a charge and fail causing an ADC to miss a creep. It's such a dumb source of toxicity in the game that could so easily be avoided.
I pull Thresh out in games every so often when the urge strikes, and every time I do I get frustrated by the fact that it feels like there is no good starting gold item for him (relic doesn't fit for reasons already mentioned, and the others don't give him the durability/sustain i feel he needs). The result ends up being that he goes back onto the inactive champs roster after that one game. I've debated just starting Doran's Shield on him and playing hella agro early game, but it feels like a gamble and I always talk myself out of it.