James Strong wrote his famous concordance in 1890, he thus could have been a pretribber, the influence of Darbyism was considerable by that time. Was he a pretribber, I don’t know, he may have been one of those who rejected Darby’s pretrib rapture, for all we know, many in England did.
At any rate, I rather doubt we can use his concordance as the last word on 2 Thess. 2:3. Like I said, the context of 2 Thess. 2 literally bristles with evidence as to what Paul meant. Not to mention men like Irenaeus, who knew Greek quite well, I’d say.
I think it’s folly to pit James Strong against men like Justin Martyr and Irenaeus. For all we know, were he to join this thread, we might find him siding with Irenaeus.
"For all the saints and elect of God are gathered prior to the tribulation that is to come, and are taken to the Lord lest they see the confusion that is to overwhelm the world because of our siin." ['On The Last Times, the Antichrist and the End of the World' Ephraem of Nisibis (Ephraem The Syrian)]