Re: "Sly's combative concepts"
I think Katherine is trying to point out that you are describing a "whotif" scenario that probably has no answer because of the way the scenario is constructed. Yes, people are vulnerable to well-planned surprise attacks. Hope for luck and recover as quickly as possible.
For me, I advocate individuals who intend to get into physical confrontation need to participant in sparring. Mostly, you need to get used to the discomfort and affect fighting has on your body - hormones, pain, injury, fatigue, vision, hearing, balance. Even the best trained sport fighters can walk into a punch that ends the fight. To consider a scenario where you first take an undefended blow (kick or punch) and then react from that is a fight scenario for which most of us are not trained.
Also, I am not sure I would say that ikkyo is always available. Nor does hands up = ikkyo. Getting up hands to defend yourself is critical, but I am not sure I am going to call that a technique.