Yes, but at the end of the day, Boras is a strawman for everyone who wants to blame agents rather than players when a UFA does not choose to come back. Agents are the perfect low calorie target when we're frustrated that a player won't accept the team's best offer and we don't want to hate the team or the player
When a player signs with Boras, it signifies that he wants to maximize his income as a player and make hay while the sun shines, and he considers that more important than the good of whatever franchise happened to draft him. That's not what we as fans want to hear, but we don't want to hate the player, so instead the easy (lazy?) choice is to hate the agent. The real decision-maker here though, is the player, and it's important to remember that.
Boras' players can and do ignore his advice and do what's best for themselves and/or the team. All Boras' schtick is really good for is preventing teams from cramming team friendly deals down a player's throat in the name of "being a team player" or some such insipidly patronizing nonsense. If a player wants to re-up, he's the boss and Boras will get him the best deal he can. If a player wants to maximize his value by trying the FA market, and we lose him because someone else decides to pay him what he's worth on the market rather than what our ownership wanted to pay -- I have a hard time fully blaming the agent on that one.