Consider the constant training Ranma went through from the day they left home until the arrival at the Tendo's. I can't imagine Genma ever letting Ranma slack off and I wouldn't be surprised if he had Ranma train for at least 10 hours a day during the 12 years they were gone.
That
really doesn't fit very well with what we see of Genma. Yes, he took him on a training trip. No, there's no sign whatsoever that it was
that fanatical. Genma even put Ranma in
school, for crying out loud, which would be a
completely antithetical action to that kind of regimen. And even later, when they get to Nerima, he doesn't show any sign of drilling him that hard on the weekends or anything.
Heck, if you look at the arc where Genma becomes that kid's pet, it's pretty clear that
Ranma is a heck of a lot more interested in training than even he is. In short, there's really no incongruity at all that Ryouga could have trained hard enough to give Ranma a good go.
Really, that's one of the things that makes Ryouga so freaking
awesome. It's not just that he's a worthy rival for Ranma--it's that he managed to get there even with all the handicaps he has.
I'm not sure that the shi shi hokodan arc is a good measure of Ryoga v Ranma's skills...
Concerning the alternate strategies you suggested, recall that their first fight doesn't actually
end on-screen. It cuts away with them fighting in daytime, and then goes to Ryouga carting Ranma home that night. And later, Ranma admits to Akane that he
wasn't holding back any in their match.
In that context, the simple inference of "not holding back"--and the only one that makes any sense, in character--is that he
tried any dodgings or blindings or whatever that he could think of. That's the whole
point--that Ryouga is good enough that he
couldn't work his way into close quarters between the ki blasts, like he does with Hinako.
(And on a particular side note, the HSH is
not an automatic-win that you can just up and blow away the opponent with, without the necessary conditions being in place. It would be a rather lame game-breaker if it were.)
As you say, we do, indeed, know from very the Bakusai Tenketsu/Horisan/Phoenix Pill/Senken fights that you mention that Ranma is willing to think outside the box to defeat an opponent. And we also know from his reactions that he's horrified at the possibility of losing to Ryouga. Not horrified of failing to learn the technique. Horrified of
losing. So it really doesn't make any sense that he would refuse to try other tactics. I mean, he had a whole
week to think!
This also isn't like the Picolet Chardin thing, where he was constrained by the
rules of the contest. Not to mention that--more to the point--you notice even
then he
does come up with yet another non-standard solution.
Thus, there's really no reason whatsoever to believe that Ranma was somehow constraining himself. It's entirely out of character with the whole principle that he fights under, and contradicts his stated desperation to win to boot.
If he flat-out
says he wasn't holding back, let's take him at his word--instead of trying to come up with excuses for him as to how he "really actually" was.