It is correct that the entire swap centers around the fearfull debuff, you are once again able to describe a mechanic correctly but not able to understand the tactic that I wrote on the first page. Using the tactic I wrote, you are however able to handle a situation when BOTH tanks have the fearfull debuff (one tank still have 5-10 s left on his debuff).
Single Taunt Guarantees aggro for 6 seconds (unless overridden by another taunt) and then you can use your AoE taunt to maintain, and build (110% of threat it would take to pull per taunt if if you were in Melee range) for the remainder of the Fearful debuff. Each 20% dip in boss health takes anywhere from 45 to 60 seconds so if necessary you can use taunt more than once on the occasion that you can't damage the bosses due to fearful.
Where you tank the bosses are different from most guilds, however how my guild and MoX, Chosen, Ace, FriendlyFire tanks it (all guilds 16man EC Nightmare) is considered one of the best ways, not the best, there might be other ways, but it is one of the best. Feel free to try it out.
I have tried it, in fact the other (well, now only) raid group does the strat the same way (tanking them across from each other, waiting for Toth to run back), but when they've done it the way I've described, they've said that it's arguably better in terms of positioning and down time on the bosses.
Edit: I understand waiting for Fearful to fall off and the reasoning behind it, and I often personally kinda wish that DPS was a little bit lower so that my Deflection and CC Breaker CDs are off by the time I get to Berserk/ Red Circles, but Fearful is perhaps the easiest mechanic in the game to adjust for, since it's not affected by RNG (from defensive stats, or where and how frequently you're targeted by Red Circles).