If you can't afford the GCD to swap to the tank, it doesn't matter because you're probably already hard healing that tank. You can swap Beacon to him when healing is less intense and you can turn your attention elsewhere.
Actually...this should never be an issue anyway, because glyphed Beacon is off the GCD. And free. And has a 3-second CD.
Disc is the spec that's most comparable to Holy in terms of frustration with a gimped toolkit: a disc priest is basically in Chakra: Sanctuary full-time except on targets they've already been healing in the last 15 seconds. Honestly, it sucks for both, both mechanics can go die in a fire, and no other healer really has anything comparable.