"4" is a pointless term. You have to stop looking at guys like pegs that can only fit one hole.
We spend most of our time lately getting Gordon switched onto smaller defenders so he can use his size and strength to get them to the rim. That doesn't change with Isaac in the lineup.
What does is our spacing. The success of Gordon and Isaac as a pair is dependent on both guys being league average shooters at worst. That's why it looked great the end of last year when both guys were hitting threes and it looked bad at times this year when both guys weren't.
This version of Gordon hitting 40% of his threes is literally the ideal match for Isaac because Gordon is built to handle the heavier stronger opponents where Isaac isn't. And Isaac covers a bunch of Gordon's weaknesses. And it sets up a situation where if Gordon is defended by 3s he can take guys to the rim but if they decide to put their 3 on Isaac he can get to his spots and shoot over them as a 6'6, 6'7 guy typically can't contest his release.
Neither guy is "better at the 4". Both are just mismatch hunters who need spacing to make that happen.