When Jesus says, the Father is greater than He is, ‘greater’ doesn’t mean different in kind or extent. It means the Three Members of the Trinity have different roles.
Believe what you will, that is your right. But being a Christian means believing that God The Father, God The Son (Jesus), and God The Holy Spirit, are indivisible, uniquely, and irreducibly God. Any teaching that seeks to lower any member of the Trinity, or elevate anyone or thing beyond being a limited creation, is just not Christian. The Bible is clear on this.
We can speculate all day about why God would choose to be ‘Triune,’ each member entirely distinct, fully God, co-equal, without beginning or end, and yet somehow be the Trinity, which is God.
We can also speculate on why God chose to have different roles within the Godhead (another name for the Trinity). No one knows why, but according to The Bible, that is precisely what they did.
So, when Jesus says that the Father is greater than He (Jesus) is, it is a matter of their respective and chosen roles. It’s not saying that God the Father is somehow ‘more God’ than Jesus, or that he is somehow better in essence.