"We like ADC diversity"

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He has a high winrate from Twitch mains and dedicated 1 tricks, and his pickrate is again.. not high.

13% is around the average pickrate for non meta adcs.

Would you say you see Jinx too much, because she's barely under his pickrate.

and 5% under his win rate

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I'm gonna stop you right there because your entire basis is faulty. Ezreal is not a generalist, nor is he good at everything. Neither is Lucian for that matter, but that's another post for another time.

What the hell? Even Riot themselves has noted Lucian as a generalist. Ezreal was king of generalists before Lucian came back into the meta, and that means Ezreal had an entire season practically to be the best generalist. Koreans loved using him all of last season and especially the beginning of the assassin meta this season. You have not been noting any historical evidence of what you're saying and you want to tell me that Ezreal is not a generalist? Think about what an ADC's most important priority is. It's doing consistent damage and NOT DYING.

When your champion has a dash on it, has consistent hard to punish damage through poke, and more importantly a global ultimate that allows your presence to fall off less when you're not in range of an objective or teamfight (with the possibility of using it as an execute), HOW IS IT NOT A GENERALIST? Caitlyn can poke early, Varus can poke early, Miss Fortune can poke early, hell even Twitch can poke early via W>E. But none of those champions use that as a consistent measure for DPS by mid game, Ezreal however does.

On the side for Lucian, he also has a dash, high sustained damage in closer range scenarios where most ADCs would be punished, and more importantly has an ultimate that has huge execute potential when used properly.

Compare this to Caitlyn for example who has the clear advantage of high range but exchanges it for low attack speed. She will do TERRIBLY against close range assassins and such unless the enemy hits a trap. That condition cannot always be fulfilled, therefore if the meta has more assassins, she will not do as well as she is doing right now. Generalists in comparison never have a bad time unless Riot nerfs them into the ground like they did to Lucian, and they are rewarded the most if their Core items are buffed since they win the numbers war through consistency.

Frankly, there aren't many adcs that really qualify as generalists, with Caitlyn being the only adc that really comes close.

With my above point, I've essentially proved to myself that you have no idea what entails a generalist ADC, you only know what is a dominant ADC and a not so dominant ADC, which anyone and their mother who doesn't even play the game can make conclusions of after seeing a couple statistics. You've confused "generalist" as "the strongest available no matter what" rather than stuff like Lee Sin who are "never bad" unless nerfed into the floor (or the respective items the champ uses have been nerfed). The only weakness Ezreal has is based on Tear usage and if the Ezreal is bad, he will likely not have it done by 20 minutes into the game. There have been many of these Ezreals and it skews his power curve more than what you're currently imagining.

In exchange, there are other ADCs that actually prioritize damage over safety and they are rewarded the most in this meta. Naturally a generalist like Ezreal doesn't use that as a primary strength, so he will not be as good.

I think you need to re-assess what a generalist is and not be going full-on stereotyping based on conclusions that are reflective of the meta and not the champion itself.