Why and How Skarner must be fixed
What is he? Supposedly a Diver. What does that mean?
First of all, let's see what Diver is.
Divers are the more mobile portion of the Fighter class. Divers excel at singling out high-priority targets to blitz toward, immediately forcing those targets (and their teammates) to deal with the diver’s presence. Divers are not as durable as the tanks or juggernauts, but Divers can take their fair share of punishment while bringing enough damage to be a real kill threat if left unchecked.
Now, does he fit the description? Is he a Diver? No. He is not even close to being mobile enough on his own, due to his W giving him very low amounts of movement speed when activated and also having low movement speed for how slow his only ability of catching up is (talking about his E). However, yes, he is very good at locking down one target in a fight but he relies heavily on his team following up because he does not do as much damage as a diver should do especially compared to similar champions like Hecarim, Vi, Rek'Sai, which all are classified as Divers. Skarner however, can be punished more than most Divers but sustainability does not make up for the lack of...basically everything a diver should have.
He does not fit the Diver description but you know what description he fits? A Vanguard's. Vanguards are offensive tanks. Vanguards lead the charge for their team and are specialize at getting action started. Their explosive team fight initiation seeks to catch enemies out of position while allowing allies to follow-up to devastating effect.
So, he fits the description especially since he does not have enough damage to be considered a Diver but he has enough sustain to be a Vanguard, can start teamfights and lock down the enemy carry effectively. Other Vanguards in the Jungle are Zac, Sejuani, Amumu, Rammus and Gragas. Other Vanguards are supports/toplaners. Now, whoever has played any of these champions and compared them to Skarner, he knows that he is weak, not in tankyness but in overall effectiveness. Every other jungler Vanguard does damage while at the same time being tanky enough to have time to deliver it. Meanwhile, Skarner, has 2 choices:
Either do low amounts of damage while at the same time being somewhat tanky by getting 
and just punishing the enemies that are out off place and possibly killing them if the allied team is nearby because at this point, even most enchanters can survive his all in.
Or
Go full tank and just tank tremendous amounts of damage but doing nothing else and why do such build to Skarner in the first place? Every other Jungle tank can do the same thing while scaling with it way better and giving more crowd control for the team.
So, what are we left with? A jack of two trades, being mediocre at both of them. The solution to this is to push him into one class either by increasing his damage, by giving him some base damage on his Q because right now, every Skarner main I have seen has told me that they are maxing E because maxing Q has no point at all. Now, someone could just say "but his Q is supposed to be a ability to help you reset sheen items to deal damage with auto attacks" and I answer that, if the only reason this ability exsists is to help Skarner proc sheen, then it should be reworked and changed with a ability that has a actuall reasoning behind it. Giving him a real Q would not only make him a real diver but would also help him into getting back in either toplane or support which Skarner has not be viable in for years. Or, giving him a base shield amount on W, giving him more speed and removing the damned ap ratio! Nobody is going to play ap bruiser Skarner! Nobody. Give him a armor scaling, more health scaling, something! But remove the ap ratio and not only on his W and E and R.
Honestly, after reading what I have wrote, the best solution would not be a rework because personaly, I have no trust at Riot's design/gameplay or whatever they are called teams and Skarner would end up something completely different than he was but, it would be a revert to the old skarner and if some people do not know what his abilities used to be, I will add them below
Old Passive Crystallizing Sting STATIC COOLDOWN: 6 Crystal Slash and Fracture apply a Crystal Venom stack on the target enemy (up to 3 times) At 3 stacks, Skarner consumes them and his next basic attack is enhanced to deal 20 − 105 (based on level) (+ 100% AD) bonus magic damage as well as stun the target for 0.5 / 0.75 / 1 (based on level) seconds. Crystal Venom and Crystallizing Sting cannot affect the same target more than once every few seconds
Amazing passive which helped him being also in a lane and made his jungling as good if not better than his current passive. All in all, very good passive.
Old Q Crystal Slash RANGE: 350 COST: 16 / 17 / 18 / 19 / 20 MANA COOLDOWN: 3.5 ACTIVE: Skarner deals physical damage to all enemies within range.
PHYSICAL DAMAGE: 20 / 30 / 40 / 50 / 60 (+ 40% bonus AD) Hitting an enemy with Crystal Slash grants Skarner bonus attack speed and bonus movement speed for 5 seconds (stacks up to 3 times) Subsequent casts within the duration deal bonus magic damage. 「 BONUS ATTACK SPEED: 8 / 10 / 12 / 14 / 16% 」 「 BONUS MOVEMENT SPEED: 2 / 3 / 4 / 5 / 6% 」 「 BONUS MAGIC DAMAGE: 20 / 30 / 40 / 50 / 60 (+ 20% AP) 」 Basic attacks reduce Crystal Slash's cooldown by 0.5 seconds (doubled against enemy champions)
Old W Crystalline Exoskeleton COST: 60 MANA COOLDOWN: 13 / 12.5 / 12 / 11.5 / 11 ACTIVE: Skarner shields himself for up to 6 seconds, gaining bonus movement speed that increases by an additional 16% over 3 seconds while the shield holds. SHIELD STRENGTH: 80 / 135 / 190 / 245 / 300 (+ 80% AP) 「 INITIAL BONUS MOVEMENT SPEED: 0 / 4 / 8 / 12 / 16% 」
Old E Fracture RANGE: 1000 / 70 SPEED: 500 COST: 50 / 55 / 60 / 65 / 70 MANA COOLDOWN: 12 / 11.5 / 11 / 10.5 / 10 Fracture old ACTIVE: Skarner launches a blast of energy in the target direction, dealing magic damage and Slow icon slowing all enemies hit for 2.5 seconds. MAGIC DAMAGE: 40 / 75 / 110 / 145 / 180 (+ 40% AP) SLOW: 45 / 50 / 55 / 60 / 65%
Old R Impale RANGE: 350 COST: 100 / 125 / 150 MANA COOLDOWN: 110 / 100 / 90 Impale old ACTIVE: Skarner rears his stinger and brings it down on the target enemy, Root icon rooting them for 0.25 seconds, dealing magic damage, and Suppression icon suppressing them for 1.75 seconds, at the end of which the target takes the same magic damage again. For the duration, Skarner can both move freely and drag the target around with him (cannot attack them) 「 MAGIC DAMAGE: 100 / 150 / 200 (+ 50% AP) 」 Impale consumes all active Crystallizing Sting Crystallizing Sting stacks for bonus magic damage. 「 BONUS DAMAGE PER STACK: 50 / 75 / 100 」 MAXIMUM TOTAL DAMAGE: 350 / 525 / 700 (+ 100% AP)
Now, if this came back, it would surely need some changes but it is way better than this R Skarner currently has.
These were his old abilities and compared to his current, are way, way better that his current kit but now I realise that Riot has never reverted serious changes and writing this is pointless. Oh well.