My problem with Hendry was a philosophical one. He was a very win now GM. While obviously some of that later was pushed by ownership, if you look at the vast majority of his early moves such as signing Alou, trading for Lee, Harden, and Nomar they are moves that are designed to win today. I don't necessarily blame him because he was a big city GM in a time where people thought that's how you ran things as a big market club. In essence, you threw money at the problem to be good every year. The Yankees did it. The Mets did it. Various other teams did.
With that being said, I've never liked this approach. It almost always leads to 2-3 years of being good followed by 2-3 years of bad. From there the cycle repeats. The problem I have with it is that getting everything to fall into place in those short cycles is exceedingly hard. One injury kills your chances. This goes into comments I previously made early in the rebuild. People often stated something to the effect of "this isn't how a big market team should operate." I always commented "Why?" The expectations were largely if you make lots of money you should throw it on FAs. That never made much sense to me. I'd much rather see a team throw money into development. You look at a guy like Torres who the cubs spent around $3 mil to sign as an IFA and compare that to what $3 mil gets you in terms of free agents and it's not even close. Of course you have to throw several years of development at IFAs and who knows where that goes but at the same time if you consistently do a good job developing players you will have trade pieces to acquire talent quicker too.
So, while I don't think Hendry was necessarily a bad GM, I don't think his philosophy was a good one. The teams that are often good for 5+ years almost always are that way because of players they developed. Even if you want to talk about the Yankees they had a core of Bernie Williams, Jeter, Posada, and Rivera combined with other additions of Cano and Soriano at various points. They obviously supplemented that with FA's and trades but the core was there.