Because one is 27 with a large enough sample size to use those numbers because they hold more weight. We are talking about is martial good enough to be the striker/CF for Manchester United and the answer is 100% no.
You then brought up in your first post “how many times has Leao scored more then 10 goals in a season”
* you inadvertently just tried to compare them their.
Then you said why did goals matter for one and not the other. The answer to that like I told you before is one is a winger who scored 14 and was voted MVP of a top league at 22. Those numbers look to be equaled or beater this season. Also martial assist don’t look that much better in the last 3 season hence didn’t feel the need to bring those up.
You are missing the point, when you big up one player and play down other by using goal stats, then the player you are hyping should have better numbers. "Leao is a winger" is a poor point, he isn't. He is a wing forward, just like how Martial is/was for around 50% of his time at ManUtd.
When you set arbitrary "20 goals" for one player, you should also apply that to other player. Otherwise you should just accept the point you are using to downplay the player is a poor one. You can rate one player and not rate other at all, it's perfectly fine but when your point is "He scored 20+ goals even once" then using the same logic, the player you are hyping score more than 10 goals once.
You can rate Martial or think he is league 1 player, I don't really care. Most ManUtd fans gave up on him and somehow he changed lot of people to change their opinions because of lack of options and his performance in preseason.
I'm not the one who compared them, like I mentioned in previous post, if you are applying some method to rate player then at least be consistent, don't come up with excuses like "he is a winger" he isn't.