Would the Christianity today be better off if Jesus never left?
While Jesus was here, even His own disciples were fighting among themselves, to see who was the greatest. And even while Satan was in Heaven itself, right in the presence of Jesus, still Satan could find ways to complain and falsely accuse people, instead of appreciating Jesus. So, having Jesus present, even doing such wonders like he did, would not necessarily make things better. Humans, because of their own conceited nature, could have Jesus right there with them, yet they judged Jesus to be not good enough for them > now, that is definition conceit, which we see now, also, how ones consider the One who is like Jesus to be not good enough for them!!
We all have been like this, somehow . . . either outrightly not considering Jesus to be good enough for us, or we have somehow neglected and even rebelled against the way His example calls us to love (Ephesians 4:31 - Ephesians 5:2); therefore, all of us need in us the correction which only God can provide > Hebrews 12:4-11.
@little stream So, Little Stream - - - part of when Jesus will come is related with when God will have accomplished all His correction and maturing of us the Bride Church of Jesus, so we get real in love, ourselves > 1 John 4:17.
So why did he leave in the first place?
Jesus came in order to die for us on the cross, and to present the gospel and reveal our Father's name. He came here in order to get the New Testament Started. But now, Devolved, we have Jesus on the right hand of the Father, in order to make "intercession for us" (Romans 8:34). Jesus is praying for us, according to His own faith, that we become transformed into His image so we are enjoyable to our Heavenly Father the way Jesus is so delighting, plus so we can benefit from how our Father loves us even as He loves Jesus > John 17:22-26.
So, Little Stream, how the prophecies will come true will mainly be how God gets us ready for our Groom, by making us real in love like Jesus is, so we are compatible with our Groom so we can spend eternity with Him!!!
So, now Jesus is our Head Transformer > Jesus resurrected is fully of God's own almighty love power flowing through and from Him to us by means of the Holy Spirit. Jesus is, then, not only a performer on this earth, but our chief transformer specialized in generating to us all that is of God in His love; and then we minister this grace even through ourselves to one another > Romans 5:5, 1 Peter 4:9-10, Ephesians 4:11-16.