Running regen yellows on zed makes him slightly more able as an energy champ, but his ratios are pretty decent so its hard for me to say where he stands (I like him as is, and would scared of a zed who could max cdr efficiently). That said, I max w>e>q on him to optimize his energy use/fight.
Kennen is tricky. Running regen yellows on him, coupled with his passive can allow for a pretty spammy scenario with ~30% cdr. There are enough stuns happening in a team fight with his ult that he can spam q to then regen more. However, in non 4 man scenarios, he feels it from the lack of regen from constant stuns going out (which is why I run the yellows that help enough for me). Some math: Q at max rank w/40%cdr costs 21 Energy to chain cast, W costs 9, E costs 44. Upping the regen then makes it easier for him to poke while still being able to escape if needed, and more regen wouldn't really benefit him when he ults a team but would help out in 2/3v2/3's.
I haven't played lee/shen/akali enough to comment there in terms of dom, but lee has always felt like a 7ability champ to me due to his resonance mechanic.
The few downsides to this is turning out cookie cutter builds for each energy champ so that cdr/regen is optimized (if you go by an itemization route). In Zed's case, currently chain casting q costs 19energy at max rank and 40%cdr. E costs 32energy at max cdr. W can be considered virtually free by comparison. What this tells me though, is if there was no regen cap, you could push to ~33%cdr and find a sweet spot regen to pop W hit E two times during the duration, and still q chain wihtout running short on energy (and basically build last whisper + brut for damage since his base numbers with W are good).
All of that was kind of back of the envelope stuff though, but I don't think it would be too hard to figure out a cap on regen, or if there is a number that passing would be useless with all energy champs at max rank/cdr (need a dom intern this winter break??? I'm already accustomed to slave labor from my undergrad ).