Their Passive I mean. You talk about how no one appreciates passives like old Soraka or Zileans. So whats the deal? The ability to give the top laner a level advantage while supporting bot is far from invisible. All the while Heimer and Fiora...
Not saying theyre bad mind you. But as far as being completely unnoticed goes..
killd0zer4 votesFiora's passive isn't under appreciated power because there's no power to appreciate.
Sozan53 votesThey don't have any "underappreciated power" in their passives - they are nothing like Zilean and Janna passives. They are just kept rather weak for various balance reasons (just like there are champions that rely a lot on their passives (Diana is the best example here) there are also some that don't rely on them nearly at all and treat them more like small bonuses (obviously Fiora and the Heimer, but also Fiddlesticks).
Sooko1 votes
5G8Nri0B541 votesI don't mind him getting touch-ups.
But I accept that he's just an archaic champion. Heimer had a rework and Fiora is more recent than Veigar is.
kirbyzama1 votesDidn't Veiger used to passively sap everyone's ap simply by being around them? That sounds op and a great example of the problem with invisible power. Still a really cool power =(
Entropy (Innate): Veigar steals 20% of each nearby enemy champion's ability power. The amount stolen per target cannot exceed 5 times Veigar's level.
BakedLotion1 votesHeimer's passive is insane for aram, and against poke champions. Fiora's is complete trash and useless while heimer's is noticeable. I actually like his passive because i barely have to use pots if im camping my turrets because i take little to no damage at all, while healing with my passive if i ever actually get hit
Teridax681 votesAs I recall, during 
's rework they tested multiple different passives, and settled with his old regen aura simply because it worked the best with his defensive siege playstyle (he can set up camp in a lane and have his allies last there for longer as well) and helped his turrets survive early poke. It's not really the most visible part of his kit, but it fulfills the needs of his playstyle in a simple and efficient manner.
When talking about a potential rework to Fiora, Guinsoo criticized her passive and seemed pretty set on removing it outright. It's not a particularly good effect (low visibility is one of its issues), and it's pretty much just there to make Fiora fit in top lane.
As for 
's pre-nerf global auras, it's underappreciated in the same way all global auras are: sure, you can level up a little sooner than normal and give your jungler a quicker level 2, and that's enough power to snowball other lanes (especially in pro play, where every competitor knows exactly how much experience they need to get to the next level), but on average it's not really power you'll ever fully appreciate, despite the massive influence it has. That's why global auras are generally bad: they're the biggest case of power without gameplay, because you make everyone on your team stronger just by existing. Because this participation isn't really active, and is diluted to work across the entire map (imagine balancing pre-rework 
's stat auras around global range), even if these global passives are valued or appreciated by individual members of your team, that valuation doesn't really come close to the massive power they actually represent, hence them being underappreciated.
kirbyzama1 votesFiora is a bad example as Riot wants to change her it just keeps getting put on the back peddle like a lot of things. (that poppy rework better be something lol) As it stands she violates almost as many design values as 
. Her E is a ball of stats. Her Q is mobility but overly simplistic. Her W is more free stats and an admittedly unique ability. Her ult is an untargetable ability that I still somehow die in a lot. And her passive is just more regen. She is needs that rework.
As for hiemer are you just talking about his passive? Honestly I don't know why it still exists its kinda weird though I guess it helps in sieging which hiemer excels at. I figure its because they are very low impact unlike zil passive that lead to a lot of cheesy top lane first bloods for no reason other than he exists. Everything doesn't need to be highly visible, especially lower impact buffs. The problem with sona was that was all she was, except she wasn't low impact and that wasn't appreciated by her, her opponents, or her teammates.