While you do make a point, there is far more thoughts needed here:

First, there are quite a few other Crusaders that can do multiple roles (and many of them also not truly at once), but have to choose one or the other, making certain gear (often selfDPS gear) useless on them.

However, let's say that Groklok (and other Crusaders) should be more fair in this regard, then let's start by having a thorough look at Groklok:

What about his other items?
If the tooth increases Eligible Receivers, Defensive Team and Gunslinger, that means he needs a change in his other 2 items too for fairness, so they become useful at "all times", both to himself and his team, no matter what role he decides to go into.

This also means he'd need a DPS buff on one of his basic skills, as he loses a +400% item, because if he kept that as well, he'd STILL be keeping an item that does nothing for him while he focuses on being a tank or support. Just for consistency you know?

Let's suggest these changes:
Football gear = All DPS item (the usual 5/10/15/40%). That's both useful to the team if he goes tank/support, and to himself if he is used as DPS.

Bracelet gear = All Health-boost item (numbers? 10/20/30/50%?). That's useful when the team needs to tank, wether Groklok himself or someone else is the actual tank(s).

That looks like pretty fair changes to his gear.

However, considering that many things in this game has that "unfairness" on certain characters and/or gear, is it really worth changing things up that much for him? Changing the gear is maybe ok (and not something I'd disagreed with at all), but how far would you go? His selfDPS abilities, they are also completely useless when he goes tank/support, should they need to change as well? And then, when looking at other Crusaders, you'd have to think similarly (if the Crusader can fulfill multiple roles, not at once, that is), which means you have a pretty massive task ahead of you.

Even me, who is quite picky in regards to these things, thinks it's a bit unnecessary to delve too deep into this issue (but still, all those suggested gear changes for Groklok would still be pretty neat, no?)

If anything, I think there are far more important Crusaders to change than Groklok. Like Sasha, still having a selfDPS gear while not even having a DPS-tag, along with 4 selfDPS skills. Or Detective/Pete/Khouri/Phoenix with 4 selfDPS skills, Monkey/Gryphon/Merci, with 3 selfDPS skills, or even Roboturkey/Pumpkin/Artaxes/Reginald/Thalia/Shadowqueen who all have 2 selfDPS skills as well. And none of them have DPS-tags.

Or what about the annoyance of gear for the active abilities? THAT needs a change, as they are really boring imo. They should work more like Trinkets, meaning if you have a gear-upgrade for Artaxes's Savage Strikes, for example, that gear-upgrade should work for ALL the Savage Strike activators, not just when used with Artaxes. That way, the gear from different Crusaders in the same seat can improve the ability in DIFFERENT ways. Like, Bubba can improve the duration of Savage Strikes. Drizzle can reduce the cooldown. And so on. Much more variety and a bit more exciting to get gear for active abilities.

So, yeah, while I agreed with you in a sense, I think Groklok has a rather small issue, to be honest.

Sorry for the wall of text xD