Interrupt without global or school silence just proves how clueless the people on the developers seat are.
4 seconds of global shutdown on heals for an interrupt would actually force healers to learn to play and finally draw a line between conscious healers and heal farm spammers.
Im a healer btw.
School silence would just put Operative even more hopelessly overpowered relative to other healers, as you can't do school interrupt on instant heals. Global silence would be overkill.
What needs to happen is that the major heal output should be on heals that are interruptible. This is how Commandoes work and how Sages worked mostly until AE heal become super fast casting. Due to PvE consideration, you'd probably need something like all instant casting heals needs to cost 33% more resources while in WZs. If you want to spam heals that can't even be interrupted, you got to pay a very significant price to do so.