Let's not "overrate" Finley and his contributions. If what Pop and fans wanted was nothing more than a spot-up shooter, then perhaps a case can be made that his tenure was suitable. However, I contend that the Spurs needed more from the position than that of a "one-trick pony", which is what Finley has been the past 5-6 years of his career.
Sure he's been a great teammate and consummate professional, but a spot-up shooter only - nothing more, nothing less. Despite that, his flaws have been glaring. The guy couldn't play defense, couldn't create is own shot, couldn't pass or make others around him better, and was a poor rebounder. He didn't suddenly devolve into this, he was this when he got here.
Furthermore, if Finley was still "all that", Dallas wouldn't have felt pressured to let him go via the NBA amnesty clause. As a max player, clearly, he was overpaid and his diminshed skills and limited on-court contributions simply did not justify his hefty salary. Of course, Cuban was a fool to reward him with a max contract in the first place, but that's another story.
Personally, after watching him decline from one of the most athletic SFs in the NBA to what he is now, I'm on record as never having wanted the Spurs to sign him in the first place. On the heels of the Spurs losing SJax a couple of summers before, I simply felt the Spurs needed a younger, more well-rounded player at that position. In the interim, they did nothing to replace the skills that Jack had or even attempt to develop a player that could mimic the tenacious defense that Bowen provided. Therefore the swing position, on the Spurs, has been in a state of flux it's been for years. While we've seen a wave of young, athletic, perimeter players enter the league over the past 5-7 years, how did the Spurs respond? They kept getting older. Once Bowen was traded, what a surprise it was to find out the roster was deficient in that area. That's how an organization gets pressured into making panic moves over the offseason.
The acquitision of Finley enabled Pop to stack more shooters around Duncan and begin his experimentation with "small-ball". In that respect, perhaps he's been just what Pop wanted. However in my opinion, he was most definitely NOT what the Spurs needed.