I think there's actually a lot of room for more tank damage, SE just need to rethink how they go about it really. A great example would be something like Turn 4 in ilvl 70-90 gear, the final phases including the fed dreadnaught put out massive quantities of tank damage with nary a tank buster in sight, it was just relentless massive and frequent auto attack damage with various similarly sized ability hits woven in to make the damage spikier and harder to predict. Needless to say, until people were overgearing the encounter, it was firmly a 2 healer workload despite the fact there wasn't a death sentence style hit in sight. By comparison, A9S-A12S's bosses hit for very little, it's not until they are throwing out tank busters or aoes that the numbers start coming at you. You could also take this further with something like the rampage mechanic from Everquest or even just cleave style attacks that need to be shared aka T11. Having a huge swathes of damage across both tanks is also a great recipe for a busy pair of healers.
Couldn't agree more, I've gotten less and less enthused about gear upgrades as each raid tier as gone by, you eventually realise that as long as you've got the HP to survive the big hits and the mp to go the distance with a little breathing room for safety, anything else is better given to the DPS/Tanks. IMHO a big part of the problem is the huge gains in VIT we see between tiers. Our best in slot HP has more than doubled through the course of this expansion. Smaller HP gains during progression would help reduce the syndrome of healer#2 feeling more like a third wheel.
Taking this point and running with it somewhat, SE have kind of backed themselves into a corner with healer DPS in that it is all terribly one dimensional, at it's most basic level, you simply apply your dots and then blast away with your biggest single target nuke. When you note that this game is incredibly vague in how it presents dot damage coupled with healer single target nukes being a bit limp across the board (I can't be the only one who misses 3.0's broil noise!) then it's little wonder that such a large proportion of the healer player base feels little inclination to use these abilities. It's not until you get to the progression raiders looking at logs and encounter data where they realise the potential since SE themselves do such a poor job of putting that across.
Personally, I think the best way forward without being too radical is to consider adding small side effects to healer DD. It doesn't have to be massive or game changing, it just has to be rewarding and have a tangible positive effect for the group beyond some weedy number flashing by on your screen for a split second. There's a wealth of options out there, small splash healing around the target you're nuking, specific vulnerability debuffs for a few seconds etc. SCH/SMN's energy drain has the right idea, SE just need to take that ball and run with it.
It's also worth refreshing the point that savage/extreme content gradually gets toned down over time via item level upgrades and the echo buff. This game most definitely caters for the more casual raider, the only real issue is that the smaller 8 man raid size means that one weak link can be a much bigger detriment to the overall raid than in a significantly larger group as seen elsewhere.
Zero DPS healers will likely always get frowned upon in the progression raiding scene as things stand because frankly, that's currently either a poor standard of play, sheer laziness or just plain not caring. However, I can tell you without a shadow of doubt that if you combine rock solid consistency, good communication, the ability to listen and learn from mistakes, the capacity to adjust and react to situations without getting flustered, a willingness to never stop trying to improve and a strong drive to solo heal as much of an encounter as is possible as early as you can reliably do so along with a DPS heavy healing partner who you can coordinate well with then you will go far.
TLDR: Being dependable, consistent and low maintenance counts for just as much as your raw healer DPS. Any group leader that stubbornly claims otherwise isn't one I'd particularly relish raiding for.