Any jungle build that doesn't involve finishing your jungler item first is inefficient. This is why the fix for tank junglers was to make a new tank jungler item, rather than say pushing the Sunfire line as an early buy.
This is a really narrow way to look at the game; if you look at S4 Rengar builds, you'd often go madreds -> mobi boots, a lot of pro junglers didn't even finish their jungler item. And this is the build that would allow Rengar to snowball out of control.
Also putting your completed jungle item on hold to buy a tear is vastly different than trying to build a whole sunfire cape; that's why they also introduced an intermediate sunfire-esque item in bami's cinder instead of just putting sunfire cape's effect onto the jungle item.
As for the part about playing around her passive better, I recommend you take Lissandra into a custom game and try to clear the jungle for a few minutes. One free spell every 18 seconds is totally not going to cut it.
I'm saying you have to learn to use it better. Or build mana regen. Her passive has built in CDR that allows her to have it up more frequently; if that's still not enough, that's why you build mana regen or take regen blues instead of CDR since you can build morello's and have 40% with magus.
As a jungler you're always scrapping together items since you have innately less gold and exp income than a laner; it's naive to expect to have identical impact as a laner when you innately have fewer resources to work with; you have to adapt to the role, it isn't just a plug and play thing. Example: Top lane Olaf builds a lot of damage, jungle Olaf builds pure tank. Jungle Lissandra is never going to do as much damage as lane Lissandra unless she's stupidly fed, so you focus on other aspects she can bring to the table, namely her CC (in which case having CDR is vital).
Some mages are high gold, high exp champions. Quite a few aren't. We run many mages as supports because they are quite good at providing utility without needing a ton of resources to be effective.
And many of them function fine currently as junglers too, it's just you have to adapt them to the role. If you're playing support Morgana, you think it's efficient for her to build sightstone? No, she could deal a ton more damage and have a ton more utility in fights by just saving that gold for a different item; the reason you build it is because it's a necessary component of that role. You bring Morgana into the jungle, you have to find a way to adapt her to the jungle instead of just expecting to play her like lane Morgana without any difference. Other elements of her kit will be emphasized, damage is most likely not the prime concern (especially since it will always be less than a lane Morgana's, as I mentioned with Lissandra, since you innately have less gold income).
Do you think it's desirable for AD to be inherently superior to AP for jungling? It wasn't always this way. It doesn't have to be this way.
I think it's really limited to think of this game in terms of AD and AP; think about your champion and why you're actually playing them in a certain role. Honestly look at the champions being played in jungle and why they're there: do you see a lot of glass cannon AD champions going in jungle? No. It's basically Shaco and Master Yi (to which I counter with Fiddlesticks and Karthus). What makes you think glass cannon AP champions should be an exception? Most of the AD champions are bruisers or off-tanks, most of the AP champions are tanks; if anything there's just a lack of AP bruisers in the champion roster (the ones I can think of are Diana, Gragas, and Nidalee; guess what, they're junglers).
This is a new problem. Didn't exist in season 4, because Spirit Stone was a thing.
And Rangers + Blue buff smite + forbidden Idol are things in season 5. There are ways to adapt to the game. If it were the case that you've exhausted every single option and still have no way of functioning as a mage jungler, go ahead and complain away, but I suspect that's not the case because I've seen mages work in jungle (I'm not even talking about just Fiddlesticks and Karthus). Yes, I know the jungle is mathematically more difficult in s5; I don't think it's so bad that you can't make things work.
Moreover, I don't really see jungle mages as an entire class as something that Riot needs to devote time and effort to blanket-supporting, especially where there are larger issues, especially since the rewards to promoting the entire class of champions seem pretty vacuous, and especially when it's still possible to make your off-meta build work given the tools available. Again, if you want a specific champion to be able to jungle more effectively, go ahead and and make an argument for them specifically. I think it's irresponsible and ill advised to have a massive blanket buff if you just want to support a tiny niche aspect of the game.
but they build Warriors.
against 
which should have been a nightmare matchup, but because of what's happened to counterjungling 
) even stronger but can still make the other AP junglers,who are struggling in the jungle, better.
(though most build her tanky) 
(good old UOL).Who are the other AP junglers?
:
I generally feel like the item is more "underused" instead of really "underpowered". If you don't need the extra gap-closing/sticking power from Stalker's or the sustain from Ranger's, but would rather like some more survivability against a specific target, you buy Skirmisher's.
and more or less all the adcs.
:Ganking
:Clear speed
:Counterjunglers
) and we are seeing incredible variety in LCS picks these days.
