The skill gap between D4 and a P4 is huge, getting a P4 player on your team would be a huge disadvantage. The gap between P4-P1 is not as significant as the gap between P2 and D4 I know it sounds small, but the gap exist.
Flame/trolling aside, D4 players are actually good for the most part. (non boosted obviously)
When they are playing at their peak they can stomp even D1-Challenger players, I've seen it and done it.
If you make it to Diamond you'll notice that the small gaps are actually incrediably large skillwise.
D4 is it's own bracket, D2-D3 are about the same, upgraded D4s. D1s challenge only for Master slots. GMs and Challengers Spank D1s most of the time.
As you go higher up tiers matter more. In gold a G4 player and P4 player are a gap, but even though the range is larger than D2-D1 the skill gap is not.
Trying my hardest not to flame any elo as all are well done achievements, but that gap needs to exist. My Brother just made it to P2, he played his first almost all D4 game, he was crushed and got demoted to P3 each time he rises back up he get's crushed again not just teammates he's not ready for Diamond, and most likely neither are you. It would be an injustice to the other 3 allies if you are a legit P4 player in Diamond, Likewise it's unfair to P3/P2 players that would be forced to play with a D4 player.