The numbers you posted with the different healers are healing that in the span of 2 GCDs. So if you cut that in half for 1 GCD, they're healing an average of about 13-15k HP. If you look at the OP's combat log, you'll see he does the Sweeping Slash twice in the span of one GCD that adds to the total of the 31k damage he took in that time frame. I don't know of a single healer that can do an average of 12k HPS single target much less two. While I agree with your numbers, those are over a longer time period. We've been having our assassin tank get hit for over 25k consistently in the span of 1.5 seconds; too much damage for any set of healers to deal with in 8 man ops.
Did he get hit for 25k in the next GCD as well? What about the previous one? My point is that the damage on most bosses looks like this:
1k > 1k > 30k!!!!
> 1k > 1k
I generally assume a 3 second burst window for any healing. But as I said, two commandos can put out 27k healing on a single target (doesn't need to be two if the boss is faced away) in one GCD. AMP is a single GCD and back-loaded, but Bacta Infusion is frontloaded. If you really want burst, casting AMP > BI is going to drop all of that healing essentially simultaneously (the flytext will precisely overlay). If you want even more burst and you have a cooldown up, Advanced Medical Probe > Tech Override + Medical Probe is even more
healing in exactly the same timespan (one GCD).
If your tank is getting hit for 25k in every
GCD, then yes, something is horrifically wrong. Even if your tank is getting hit for 25k in back-to-back GCDs, then something is probably wrong. However, I haven't seen that happen on any content to date without some other mechanic being horribly screwed up (e.g. NiM Kel'sara on a tank with 7+ stacks).
Burst windows like this are precisely why tanks have HP in the first place. During the lull moments, between spike attacks, healers should be trying to push tank HP back up into the 80-90% range (no point in going all the way to 100%, and doing so can cause overheal issues with shadows). During the burst moments, tanks can fall down into the 20s and 30s if it's a really sharp burst, but healers have lull moments immediately thereafter to catch up. As long as their attention isn't divided by numerous targets taking damage during the lulls (which does happen), it's pretty easy to repeatedly prop up tanks for these heavy hits.
Incidentally, I found one of my logs from a week or two ago tanking Corrupter Zero (not our main group, incidentally). http://www.torparse.com/a/459162/37/0/Damage+Taken
Sweeping Slash hit me 6 times (total). Unshielded and undefended, it hit for 8759 damage. Now, only one of my armorings is 72 (the rest are 75 and 78), so I'm definitely going to mitigate more of that hit than most shadows, but the point is that it only hit 6 times and the healers (which were not our main healing combo) were able to keep up with the spikes.