I'd say that it's the uptime; the ability to be Power Boosted just compounds the issue.
Just look at Mind Link on the Arachnos Widows - it's 10% defense, 5% to-hit, and 30% psi resistance for 90 seconds; the recharge is either 4 minutes or 5 minutes depending on which direction you go. Many builds (especially proc-heavy builds) don't perma this because it actually requires some investment in recharge set bonuses to get there. The psi resistance is nice (seriously, a Widow with Indomitable Will and Mind Link runs a 40% psi resistance unslotted) but it also means that it can't be boosted. And yet despite being around for much longer, I haven't heard anyone complaining about how strong Mind Link is.
Farsight has the same as the lower of those recharges, but lasts for 120 seconds, making it trivial to keep perma before even taking into account Chrono Shift. I'm against lowering the defense because of Dispersion Bubble, though - Dispersion Bubble also grants mez protection, which Farsight does not.