Not sure but as a healer, atleast i am doing this, i have prio list and DPS are on this list is nr 3, tank are 2 and healer are 1. I let you die if you are not in this list on the top and the other two needs attantion or if you are in so rough shape (vuln stack man baby) that letting you die and rezz you is cheaper.

"Tunneling damage" What on earth is this ? As a healer you have AOE (1 Button) and single target (1 Button) plus a DoT (1 Button) and you have a OGCD thats it. There is nothing to tunnel here. If you are tunneling dps than, lets be honest here, you have clearly other problems and you should LEARN the healer job FIRST.
Furthermore PLEASE STOP with "all healers" or "many healers" are like that - thats just untrue.

I am not sure were you get youre healer guides and stuff because all sources i know of worth their SALT will tell you the following - READ your TOOLSTIPS and LEARN your Kit first, learn how to heal and learn the conent you are playing AFTER THAT you start minmaxing your DPS as healer.

The forum these days has a lot healer-hate -,- please stop it. The world is not Black and White and taking stuff out of context is BS and most responses here just that. OP discribeded a situation were OP just overhealing like crazy and complaint "why my co-healer not doing same ? ". Thats not a carry nor it is top notch healer gameplay. If you are not good or cant heal and DPS - thats completly fine - if somebody harasses you just report them.