I will leave the Greek to people more competent at Greek than I am. All I will say is that I don’t really see a “For” starting the sentence in Hebrews 2:5 when I look at the Interlinear and how that was structured. That said, I am wired by our creator with some talent for spotting patterns and wanted to offer what help I could.
Starting at Hebrews 1:4, we see the first mention of “angels” and a transition to a discussion whose basic “theme” is LETS COMPARE JESUS TO THE ANGELS. (Hint: Jesus is much better.)
This “Jesus rules but angels drool” comparison runs from Hebrews 1:5-14, where it concludes with the observation that angels are just the ‘gofers’ for God’s plan to save people.
Beginning in Hebrews 2:1, the SUBJECT abruptly shifts gears. No longer is the author talking about a comparison between Jesus and Angels. Things suddenly got VERY PERSONAL as Hebrews 2:1-4 talk about US. Specifically, we are being warned about the consequences of ignoring what God and the Angels and the Holy Spirit have all TOLD US. We are the subject, not Jesus or angels.
At Hebrews 2:5, the subject abruptly shifts back to angels and Jesus. Where Hebrews 1:5-14 focused on Angels vs Jesus as God, Hebrews 2:5-8 (ish) focuses on Angels vs Jesus as a Man (the second Adam).
Given the Jesus-Angel to Man-warning to Jesus-Angel structure of the basic SUBJECT being focused on, I can see how the link between (or jump from - to) Hebrews 1:14 and Hebrews 2:5 might be “implied” by the structure even if it was not explicit in the grammar.
So that’s my 2 cents.