Talk about being picayune! There is no significant change in meaning with the two translations of that verse.
"is come" vs "coming" is a huge difference. They are opposites.
I know you want to squint your eyes and pretend "coming" doesn't mean the future, but me and the dictionary disagree with you:
com·ing
ˈkəmiNG
adjective
1.
due to happen or just beginning.
"work is due to start in the coming year"
synonyms: forthcoming, imminent, impending, approaching; More
2.
likely to be important or successful in the future.
"he was the coming man of French racing"
This is Darby's translation of 1 john 4:2:
"Hereby ye know the Spirit of God: every spirit which confesses Jesus Christ come in flesh is of God."
That's typical of the twisting of scripture Darby does. He changed the KJV's words, and defied the intent of the Greek, to stop 1 John 4:2 from clearly pointing to Christ's first coming. The best I can say is in this kludged verse, at least Darby avoided the word "coming" which forces a future meaning. You can argue it's literal, but that argument ignores Greek style of using present forms for past events. And, you can't make the augment that Darby was blindly following literalism when he uses the word "coming" in 2 John 1:7