How do I know that teams weren't offering a first round pick? Because we didn't trade Buch for a first round pick. I can believe that Drury was overly conservative and didn't want to risk holding on to Buch to get more later because of the potential for injury. But to believe that there were 1st rounders galore being tossed like singles at a strip club, only for the GM to say "hmm, no, I'd much rather a 2nd, because 2 is MORE than 1!" He's an NHL GM, not a Pakled.
As for the draft odds, again, I know the odds are high (though I don't think it is quite as low a percentage as you have been saying). That 15% number I think comes from Doug Maclean's piece, where he found that, over a ten year span, only 15% of 2nd rounders became impact players. He found that 25% of 2nd rounders become solid NHL players (he was also a lousy GM, so there is that).
Looking at just the NY Rangers, even in our worst stretches of drafting, we do better than 25% in the second round. From 2005-2014, the team had 9 picks in the second round. They hit on three of them (Michael Sauer, Anisimov, and Derek Stepan) as NHL regulars (2nd line/2nd pair). Two others (Marc-Andre Cliche and Boo-Synergy Nieves) made it to the NHL for shorter stretches (151 and 76 games, respectively). Christian Thomas got a couple cups of coffee (25 NHL games) and only three of them (Antoine LaFleur, Ethan Werek, and Brandon Halverson) busted completely (though Halverson did get one game, and we were able to move Werek for the best three years of Oscar Lindberg's NHL career). So in one of the worst 10 year stretches of drafting in recent team history, they got impact players with 33% of their picks, got three fill-ins/plugs with another 33% of their picks, and busted on the final 33% (though they were able to spin one of those busts into a role player). Two of our most recent 2nd rounders, Robertson and Cuylle, are among our top prospects. TL/DR--the odds of landing a useful player on an ELC with a 2nd round pick are high enough that it's always a good idea to pick up a spare pick whenever possible to increase those odds even further.
Finally, I'm not rationalizing or excusing anything. I didn't like the trade. I'm not thrilled about the current situation with Kravtsov. What I am doing is getting past that disappointment and trying to get excited about what we actually have. Same reason why I'm excited about Robertson rather than being emo about losing Zuccarello. You want to live in the past and give yourself an ulcer over something you can't change? Be my guest, but I don't understand what anyone gets out of that approach.