Interesting. Just out of curiosity:
(1) Did you yourself memorize all 832 pages (265 + 303 + 264) of the English version?
(2) If yes to (1), how long did it take you (and how old were you) ?
(3) If yes to (1), did you reach KGS 5d at least with zero help outside of memorizing Ishida?
(4) If no to (1), then you must know at least one person who has memorized Ishida, and with no other help, reached KGS 5d?
(5) What exactly are you guaranteeing with?

I guarantee that you would reach KGS 15k.

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

It seems that if joseki knowledge was the only prerequisite to 5d, then programing a 5d computer opponent would be quite easy, so this is obviously not the case.

If we broaden fantan's statement to mean that if you memorize the entire dictionary while actively applying the josekis in games and learning other higher concepts through these games, then I am willing to give it a little more weight. It is impossible for a human being to completely isolate himself from all aspects of the game except joseki, so I think it is fair to assume that additional influences and connections are being brought to play in this hypothetical scenario.

Thanks for all of the responses, everyone. Interestingly, when I came across this situation again (opponent plays kakari on his first move), I played tenuki on one of the other corners, and within a few moves had a substantial moyo on the top and left sides. However, I ended up losing the game by resignation after a couple of successful invasions by the opponent, thereby destroying much of my potential territory. This was one of those games where I just played horribly, and got totally destroyed by a relatively equal opponent, despite the optimistic opening.

Go is one of those games in which I start to gain a bit of confidence, only to nearly have it destroyed after a bad game/s. Yet I keep coming back for more punishment It is very easy to get frustrated with this game. However, it seems like the fascination with it outweighs the frustration of the steep learning curve.

(1) I didn't. I only memorized a small part of it.
(2) Still it took quite some time but that is because I am old.
(3) I reached KGS 5d with (1) and a lot of help outside of it. But if I had to do it over from the start, I would just go ahead to memorize Ishida.
(4) No. I haven't seen many things (e.g. the very existence of you!) but I know they are true.
(5) ...

The bottom line: memorize things, parctice what you memorize, reflect on it! I know this is hard. But the point is that people tend to approach Go as an art, thinking they can learn the philosphy and then win the game. Really one needs to put in hard work into it. A mayo is nothing before you know how to defend it. There is no shortcut in life. This applies to Go too.