If that wasn't Harvey Smith's fault, great. Then explain whose it was.
Couldn't blame be assigned team-wide? After all the IW development team, with a few minor changes, was basically the same team that made Deus Ex. You seem to have latched on to the change in project lead (From Spector to Smith) but if you're familiar with the role Spector tends to play in game development, you'll see that that wasn't the driving cause. Spector does not handle the nuts and bolts of development. He often gets credited for the success of Ultima Underworld and System Shock 1 but those games's design can largely be credited to Doug Church; Spector's role was, and continued to be with DX, largely managerial. Granted a good manager can make a world of difference, but in terms of hands on design decision making, that has never been what Spector has been involved in.
I don't know of any Ion employee that has, post-Ion, said that they were really pleased with the development of IW. Harvey Smith, among others, has made it pretty clear that they were not happy with the final product. What left such a sour taste in the collective mouths of the IW development team was all the problems that they had with the developing their own engine tech. Early on, they had made the decision to create their own next-gen engine, and to build that engine around the kind of gameplay they wanted to achieve. Fairly late in the development cycle, however, it became clear that the technology base they had built was not going to be able to support what they wanted to do. In fact, the engine was so broken, they asked Eidos for the time and money to scrap the existing engine and start over on the technology front. Eidos obviously hasn't been doing well since the late nineties, and simply did not have the money or the desire to fund such a significant development delay. As a result Ion had a broken engine, a bunch of features that weren't working right, Eidos' demand that the game be multi-platform, and a release date less than a year away. The focus became less on creating a polished product that was worthy of the Deus Ex name, and more on finishing a game that was at the very least in a playable state. To do that meant cutting a lot of features, content and corners in a mad rush to get something, no matter how disappointing, out the door.
So who then do we blame? Is it Eidos, for not funding a delay and demanding that the game be multiplatform? Is it Spector, for not lobbying hard enough to keep the game PC only and to secure additional funding? Is it the programming and engineering stuff, for developing broken technology? Is it the designers for making the wrong decisions on what to cut, and how to implement what wasn't cut, in the rush to get the game out the door? Or was it Harvey Smith for presiding over the whole mess?
I think it's fine to assign the blame to Smith as he was, after all, the project leader and therefore ultimately responsible for the finished product. That said I think it is unfair to characterize him as incompetent or actively trying to develop a game that wouldn't please the originals fan base. The development cycle simply went very badly wrong, for all of the above reasons, and given the circumstances I think the Invisible War that was released was about as good a product that could've been salvaged from such a cluster fuck of a development cycle; I doubt that, if someone other than Harvey Smith had been at the helm, we would've gotten that much better of a game.