Probably wrongly. It is suggested by some commentators (eg Hyam Maccoby) that the Synoptic account of this gore feast is derived from Paul. John gives a different version.
Meh. I answered the question that was asked. Yes, I would read
Mark and Paul, and conclude that the same Jesus was intended in both places. If that happened because Mark copied off of Paul's paper, then plagiarism is the surest sign of agreement about meaning.
If I had been asked about
John and Paul, then I would have noted that
John lacks both the institution narrative and a distinctive teaching about remarriage. I would still give an affirmative answer, but the argument would be indirect, your choice:
- There are enough points of resemblance between the synoptics and
John to think that they intend the same Jesus, and so, if
Mark and Paul mean the same guy, then so must
John mean the same guy as Paul.
- There are parts of
John that seem to me to be commentaries on Paul, and not all of them flattering. This would suggest that the two authors are discussing the same underlying situation, and would lead to an expectation that they would say different things about it.
I see no basis for thinking that John was unaware of the earlier Last Supper narratives.
John has
Mark's disclosure of the betrayer by dipping in the dish, for example. So, if John didn't include a bread and wine episode, or the instruction to do just that as a personal memorial (part of Paul, but absent from
Mark), then that was his literary choice. Maybe his church wasn't one of Paul's, and John's church did foot washing instead.
Who knows? Maybe John was part of some weirdo heretical "No vampires, no cannibals" cult.