Fun is relative to the person. Everyone hates losing so that doesn't count either. And personally out of all the listed champs, only some are actually hard to fight.
GP has to make a choice early on if he wants to go damage or tank, since he won't usually get a chance to change, he is annoying to fight as melee due to barrels but if he can't get his barrels off, he loses to any top laner since barrels are majority of his damage.
Garen I feel like I have beaten the dead horse enough already so I am just going to be blunt. He lost his W tenacity and most of the tankiness from it, his Silence on Q was lowered, his MS was lowered as well. His E does less damage til 16 when he spins enough times to outdo what his old E did. His R is technically not different at all. It just can do true damage if its on Villian which is irrelevant since when he uses it it will already kill the person due to excute damage. So overall he was nerfed due to the Juggernaut remake, he is easily the weakest of all of them.
Skarner....there is a reason no one plays him anymore....just saying.
Morde I am mixed about, with an aggressive support he is pretty tough but without one, he is a joke. I oftentimes even with a support like Thresh or Leona only lose to him due to Dragon, without it he isn't too overbearing and he falls off extremely late game. But this one is questionable.
The last 3 you mentioned are indeed annoying. Darius is most likely going to get nerfed hard once Worlds is over so I don't worry much about him. Fizz sadly has always been like that but at least the bright side with Fizz is once he is down, he often stays down, unlike say Yasuo which can feed 10 kills but if he manages to get like 2 kills, will be able to penta the enemy team due to getting the only 2 items he needs. Ekko I feel is too safe but at least bright side with him, he is only a threat as a tanky jungle which doesn't do much damage, if he builds pure AP, he often has to waste his ult in any fight at all or won't even be able to cast it before dying.
Mainly the 2 problem childs I feel are Darius and Fiora, Darius since he is meant to be a lategame monster that excells at teamfights, but he is also extremely dominate during laning, even if he doesn't kill you, he can farm his way to near invincibility. Fiora I can't even explain that hot mess.