Christianity started with Christ, not Constantine. And back then they didn't keep Easter. They kept Passover.
Easter was not for Christians ..
Horse hockey. You confuse a name with an event.
The name reveals (indeed betrays) the pagan accommodation. Which reminds me of another holiday, but that's another topic.
And Christians in the east call their Easter, Pascha - from passover. The connection between the Jewish Passover and the Christian feast of Easter is real and liturgical.
There are many similarities, but they are not the same. Christians celebrate the resurrection of the Messiah; Jews do not. Neither are pagan.
Yes, and we have history of a debate over when to celebrate Pascha/Easter back in the early second century; long before Constantine.