Of course they could be doing this instead, as long as Gon's head is strong enough, as well as his reinforcement. You actually SAW it being done in the manga by multiple characters, you know?
You also seem to assume Ken is some kind of mana shield as opposed to a general modifier, that Ken means X damage absorbed from anywhere so as long as you got enough AP left you're more or less invulnerable to hits that deal less than X damage, even though HXH shows that weak points in the human body clearly exist. Head + Ken is not the same thing as Fist + Ken. During Gon and Killua's practice at manipulating %s for attack/defense it went something like:
Killua: 80% on right foot
Gon: Guard with 85% on left hand
In your world they could be doing this instead:
Killua: 80% on right foot
Gon: Guard with 85% on face
No, you just are assuming that gon's aura is much, much stronger than it actually is. It was pretty clear in the fight between Gon and Genthru's fight that Genthru's actual Apparent Aura was MASSIVELY stronger than Gon's. By Apparent Aura, i mean 'actual aura power' there:
Actually I noticed that screenshot shows some outright contradiction. Gon did 0% one hand, 30% other hand, 70% feet versus Gensuru which is 25% right hand, 25% left hand, 10% rest of body, and an implied 40% used for Little Flower.
Since Ken is 50% everywhere then clearly that attack would've been guardable by just doing Ken, except Gensuru stated that Gon cannot guard 2XLittle Flower and that seems like a reasonable assessment of what happened in the fight. Gon already knows Ken at that point, and Ken is a simpler state to maintain compared to any other non uniform state, so if Ken is sufficient to defend against Little Flower there's no reason for him to do anything else. Gon's weakness, at that point, is his inability to sustain aura extendedly or move it quickly. However, Ken is the easiest state to maintain out of all possible distribution of AP, so it'd still be best to simply stay in Ken the whole time. Given Gon's max output easily exceeds even a Spider tier character at that point (Gon is the only person who can knock Razor back with the dodgeball), his Ken should not be any weaker than any Spider-tier character's Ken (he'd have problem maintaining it, but that's a different issue).
So therefore the conclusion you get is that Little Flower can penetrate Ken and has to do at least 150 points worth of damage.
It only did damage to Gon because this Gon had a low-level aura yet (Chimera arc Gon would have had no problem noping it).
You seem to assume that just because Little Flower doesn't seem to have a physical component that it does not use the base '100', and that it somehow does less than 100 AP worth of damage, which is less than Gensuru's fist without aura. Yet Little Flower blew up Gon's hand when he didn't shield it with aura, and Gon is someone who can break Ilumi's hand with his physical strength back in the Hunter exam. Just because Little Flower does not have an apparent physical component doesn't mean it does less than 100 points of damage, otherwise it's literally pointless to have a move like that and it should have done no damage to Gon if it is so weak.