Well, Lee has literaly 0 energy problem even if he misses his spells, and the fact that he is very forgiving on this side is one of the many reasons why he is the first jungler picked basically any time he is available. If Lee misses, for example, his Sonic Wave, is just enough that there are a pair of jungle monster around to quickly regain energy (especially true when Lee players try to gank on mid lane from raptors camp). And he can basically cast abilities for free if he can sneak the pair of AA to regain energy in between of the second cast of his abilities and unleash the full combo which energy cost is really manageable if you can even sneak 1 AA after every ability
Akali has 0 energy problems too unless you are turrible with her
Zed, well at least you got to hit twice the enemies with your shadow, so if you miss him or the enemy is capable to kite you you could get in some light trouble from time to time, but really he is forgiving too as his full rotation cost is kinda low and allow him to cast another Shadow and use another ability to regain energy before running out of energy(and really, you are missing almost 2 rotations to go out of energy)
Kennen...well, I disagree, he is energy gated some, imho . Given that his CD are very low, he can't afford to use his abilities all day long as Akali/Lee can if he don't proc his passive and/or he got to use Lightning Rush defensively to escape instead of using offensively(and here, look at a lee that can jump with his Q on a jungle camp and restore energy while escaping with a pair of AA), and he needs to hit enemies 3 times to do that, so even with the low CD if he miss some ability or waste Lightning Rush(for energy restoration purposes, of course) he run out of energy and has to wait some(and his QWE combo has higher cost than Akali/Zed, as a matter of the fact).
He is least forgiving of all the three champs mentioned above, really(another of the reason why he is maybe the only example of energy/no resource balanced champ, he is not THAT forgiving if failing to regen energy)
Shen yeah, we all agree on him, even riot agreed and hlped him a bit in the last patch. i think the core problem is the fact that, aside from hitting or not his taunt the energy regain is tied more to Feint and aa instead than to Vorpal Blade, which is non sense. If Shen is using Feint he is probably in a situation when he has trouble autoattacking because he has to survive first, and he can't even use Vorpal Strike often to regain health if the battle extends, so he can't effectively recover enough energy through Ki Strike
If Shen uses the taunt towards 2/3 enemies, but only hit 1, and has to Feint, 110 energy is yet gone, he can use 1 Vorpal Strike to sustain a bit longer, and then he can only use after a pair of second either 1 of Feint/Vorpal Strike until Ki Strike goes off CD(and if enemies caught Shen while he was splitpushing when he just AA a minion with Ki Strike up and apply some form to CC that impede him from AA he would need to wait for a lot of seconds)
Ki Strike Cd reduction should be tied to Vorpal Blade too, not only to Feint, if they want to put Shen on par with the other energy champs. Like, if Shen hit with an AA an enemy marked with Vorpal Blade Ki Strike is reduced by an additional 0.5 seconds(stacking with Feint Ki strike CDR