Well I did say in my post that I, like most tanks, will use the first pull as a measure of what the group can handle. Also lets be fair, the way dungeons are structured your generally looking at 2-3 *pulls* between each boss due to gating. Neverreap - First island is generally 1 pull. Thats my guage. Slow kill I'll split the second island into 2 pulls, good rate next island is a single pull etc. I'm not arguing that there are not tanks out there that try to split pulls as small as possible. Hell I read a thread the other day about a tank who single pulled the trash in Fractal /boggle.
For a tank to pull that small there really has to be a reason. Not comfortable with the instance. Not comfortable on the class. Dubious of other party members (Healer / DPS) Communication is key here. Ask the tank why they are pulling light. If they have a reasonable answer, *I'm new here* you can either deal with it and talk to them about the pace or leave. As I said in my post, Healers who DPS I love, but I never expect it going into a DF. Unfortunatly you will get new tanks or fearful tanks in DF. I'm just saying that with an experienced tank, pace is a group effort and not something a tank alone can control. I've been in many DF groups that run 20-25 mins and just muttered to myself about DPS not pushing hard enough. Its DF though you take your lumps. I'll pull as fast as the group can handle, I love sub-20 min clears. However in DF I generally find my clear time is around the 22 min mark .. and the DPS run sub 800 over all DPS numbers, which is tragic with the amount of AoE that can be done on trash. (Yes I'm talking about SMN and BLM too here)
Your point seems to be that in a capable group that's pushing high DPS and killing fast, the tank can hold up progress by adding wait time between packs. Yup that can happen, probably because of one of the reasons I've covered, maby the tank is new and is'ent confident with the instance and wants X CD up before he pulls again. There's alot of reasons a tank would be slow.
Bottom line, if the tank is waiting between packs the best way to deal with that is to talk to him/her. Pulling ahead wont work for a tank who's already on edge because they are new. Tanks tend to get alot of heat when they mess up, it tends to make new tanks alot more cautious, talk to them, encourage them to push harder and reassure them that your not gonna go apeshit if there is a problem and a wipe. Hell its how tanks get better, some personality types wont deal well with you pushing them without at least some encouragement and reassurance that a death / wipe is not the end of the world.
I've played tanks since DAOC back in 2004 (I was a Druid in EQ O_o) so I'm comfortable with the role, and I tend to join games with friends, friends who dont mind my pushing to limits and getting them killed a fair bit to learn those limits. Not everyone is as lucky and I would imagine that leveling a tank through DF alone with random people all the time can be very daunting for newer players. A bit of communication and compassion goes along way to ease the tank queue and get more tanks in there.
So *how do you deal with sluggish tanks* .... HELP THEM. (Yes I do queue as DPS at times, and I do practice what I preach ... I help them !!)