Consider though, which characters would use exclusively holy symbols for attacks.
Clerics and Vampires.
Paladin's would also need to use a weapon for most of their attacks. Avengers as well. Anything else needs to be hybrid or multiclassed into one of those classes to get access to implements. So, outside of two classes, you aren't really using the weapon repeatedly, and the vampire is one of the few that would actually get involved in melee. Giving enemies a situational -2 to their attacks against you (and denying them access to some of their striker damage) is good, but increasing forced movement is nothing to sneeze at either.
Heavy blade expertise ... yeah, that one kind of sucks. But then again heavy blades are pretty much the easiest weapon to pick up because of their +3 prof and other feat support. The Axe one is also pretty lame, especially with three axes being brutal anyway. The bonus to damage ones are pretty good, and they do fit the people most likely to use them (rogues like light blades and c/a, spears tend to be part of charge builds, and at least assassin's and vampires thematically target bloodied enemies, if not as good a fit for monk's).
Part of the equation is that weapon choice for most classes isn't decided for you, but implements are less so. So the benefit for the weapons are probably not as strong as the implement ones in general.
Oh I definitely get that, don't get me wrong. It still seems though that even if more or less restricted to two classes, the feat seems pretty strong. Consider conditions like stunned, dazed, flanked, prone, etc. will not grant CA either if I am reading it correctly (though stunned at least would likely start inflicting it once the character's turn comes up since he or she could not act).
Also, isn't the holy avenger considered a holy symbol? I believe this would allow pallys to get around it (realizing of course that we are talking about an epic level rare item). Cunning bards could also have a field day with this by using the Star of Corellon, and multiclassing isn't exactly a burden for bards.
The point about weapons vs. implements is interesting though and something to consider.