By your standards maybe. In accordance to the official Type-0 info, Deuce would be the "smallest" you're referring to, not Rem. Deuce is not only 2 centimeters short thereby making her the shortest, but also younger than her, and she dances around the battlefield playing a flute. How that does not say "smallest" and "most vulnerable" to you, I don't know, but that is your opinion and I respect that. But seriously, you need to make it a point in life to point out what you say is opinion, what is fact, and what is talking out of your ass.
You have an absolutely shitty way to express your feelings in regards to female characters, only referring to their appearances in the process until for instance, when I called you out on it on your on profile. And you are missing the point. It doesn't matter whether the character they "kill" is male or female. In response to your logic, why don't they kill of a male character instead? Why not Ace, or even Eight? I imagine that your response would still be the same. And again, you don't know if she's even dead. I personally felt more sad for Izana, a character we don't even play as or even know asides from the fact that he's Machina's brother, than I do for Rem, but at least I care about them both equally. Whatever reason Tabata had for choosing to do these things had a perfectly good reason, and what's done is done.
In the first trailer for this game, back when it was still being developed for mobile phones, there was a scene in which Ace appeared to have died. Would you have cared for him as much as you do for Rem? Would you have cared for any other character, even if it was someone as insignificant as Aria or Naghi, as much as you do for Rem?
The actual thread in which that Shiki response lies tells a different tale. Besides, we've probably spoiled the entirety of TWEWY for you by answering all of your diddlying questions :\ We also explained Shiki's character in extreme detail.