+1. From what I've seen, lacking said "anchor" role can cause all sorts of pain, even just for burning groups of trash. E.g. a grouped pile of mobs suddenly decides to focus on one DPSer, and one-shots them. Or they escape with a sliver of life, and run around scattering mobs behind them.
If a particular run is most efficiently done with a 5 DPS group (I have not seen many of these), then obviously having a Strife guard is a waste of DPS. If you need a tank for anything, Strife's build is as good as any for that specific purpose. I would argue that if you wanted just one group composition to run everything, having one member with lower DPS ("GK=50% more" -> "Strife=66% of max potential", which is still decent) is less of a tradeoff than missing an anchor when you actually want one.
Anchors aren't necessary if your party is competent. They're not necessary if your party is incompetent, either, so either way you're just giving up DPS for no discernable benefit.
Plus, "anchoring" doesn't actually make any appreciable difference. It just feels like you're taking more aggro because you're actively trying to get hit, but it's not like the mobs are actually targeting you any more than usual. In my experience, 95% of aggro is determined by a combination of DPS and being in melee, which means the melee warriors/guardians will always take the most heat, while the guys in back take less. Toughness and vitality only really help if the other factors are otherwise equal. If you're actively giving up DPS for more toughness, odds are you will actually pull less aggro, not more.