Hold it! I have a hard time believing you don't know these passages in Revelation 13: 16 are written in Greek! It wasn't written in Hebrew.
The Greek word for hand is,
cheir: the hand
Original Word: χείρ, χειρός, ἡ
Part of Speech: Noun, Feminine
Transliteration: cheir
Phonetic Spelling: (khire)
Definition: the hand
Usage: a hand.
The Greek word for ARM is,
brachión: the arm
Original Word: βραχίων, ονος, ὁ
Part of Speech: Noun, Masculine
Transliteration: brachión
Phonetic Spelling: (brakh-ee'-own)
Definition: the arm
Usage: the arm, strength.
He didn't use the word Brachion in Rev 13: 16 which he would have done if he meant the arm. In Lk 1:51 they used ARM (brachion) when they meant arm. That's the greek rendering. Yes in Hebrew arm and hand can mean the same and you'd have an argument if you were talking about Old Testament text. Not for the New Testament though. So I think it's willfully misleading to try to mix the two to say well it just all means the same thing. NOPE it doesn't! One language is limited and hand/arm can mean the same thing but the other language it doesn't.