[Mrs. Don-o]

I think you're making a good point there. The circumstances had definitely changed, and that contrast is being pointed out in Jesus' explanation. The grammar --- as you rightly say --- shows this.

Nevertheless, Jesus demonstrates that he did not need guys with swords to keep the soldiers at bay: He could do it with a word. (John 18:6)

Second, He actually says the purpose of the swords is to fulfill prophecy (Luke 22:36):

"... if you don’t have a sword, sell your cloak and buy one. For it is written: ‘he was numbered with the transgressors’; and I tell you that this must be fulfilled in me. Yes, what is written about me is reaching its fulfillment."

[aMorePerfectUnion]

“Second, He actually says the purpose of the swords is to fulfill prophecy (Luke 22:36):”

No.

He is saying the disciples would now need the 3 items (not just swords) I like in the past, because being numbered among the transgressors was going to happen and it would radically change their previous experience.