To Rav Avraham Abulafia, Jesus was a very great tzadik. But that does not say anything at all about Christianity. Rav Abulafia quite definitely considered the Catholic Church to be straight idolatry. and in that he was going with the opinion of the Rambam. However Tosphot in tractate Avoda Zara considers Christianity to be ''shituf'' (joining anything with God's name ).[Actually in that one short Tosphot there are a few opinions, but the general gist of his argument is that it is shituf.] [Shituf is joining another with God. In the Gemara itself over there, it is talking about the prohibition of joining anything with God's name in an oath--for example when Gideon shouted ''A sword to the Lord and to Gideon'' to arose his men before battle.

Rav Avraham Abulafia lived near the time of the Rambam. The Rambam died in 1204 and Rav Abulafia was born around 1240.