You seem to be basing not being able to use procs before another tick of flameshock on single target. Where in arena (3v3 for my purposes) you will have 2-3+ shocks out at any time, meaning that overlapping ticks do occur. As for my "arbitrary" 35%, that is a dot break point for flameshock and since it is easily obtainable you aim for 35% "in pvp". Gaining more haste for faster ticks is only beneficial if you are only dotting one target where ticks cannot overlap during a global. An extra dot tick is not all that beneficial since they get dispelled/ reapplied but you get so close to break point just with base stats from gear that it is worth it to hit 35%.
If overlapping occurs like you said, then breakpoints mean NOTHING. Why are you aiming for it? What does it do for you other than sate your need to reach some sort of "cap".?
I have 37% haste currently. FS ticks every 2.18 seconds - if it is on 2 targets, this is on average, assuming 100% uptime, 1.09 seconds. On 3 targets it becomes 0.73 seconds.
As Lava Surge chance is a constant (20%), we can work out the average time between procs if we assume 1 proc every 5 ticks. (Yes I'm aware this is not ideal, but it will do for these purposes)
At 37% haste (my character);
1 FS = LvS proc every 10.9 seconds
2 FS = LvS proc every 5.5 seconds
3 FS = LvS proc every 3.63 seconds
Going up to 50% haste (I think the max you can push out is 52% ish as a Goblin with full haste gems + BS/JC, but whatever), each tick is down to 2seconds.
1 FS = LvS proc every 10 seconds
2 FS = LvS proc every 5 seconds
3 FS = LvS proc every 3.33 seconds
It's still going to be a rare occasion where you get procs overlapping, and chances are you could be using them faster anyway.
Also, as was shown on the other page be Forumz, Mastery like Crit, gets worse the more you get of it. This is not the case for Haste which only improves.
And yes you reduce RNG by making procs more consistent as you said, but this is the same case for getting more haste anyway.
A final point is alluding to the fact of maximum burst. If you truely want to global people, you would gear Int > Crit and take Ele Blast. Crit for Elemental is a 2.5x modifier (2.58 with PvE meta gem), and you could see 150k Ele blasts into 100k Fulminations.