i have good and bad news for u...
there is only 1 elo range that does not spam op champs and thats the 1400-1600 range. this elo range is good enough to not be low elo but still dont abuse things to get to high elo. you'll regularly see only 3 or 4 revives in a game and very rarely any of the op champs. besides jayce, the op champs are actually not very fun to play.
tryhard hell starts at around 1600. you will see an op champ or 2 in every game and most people have revives. 1600-1900 is by far the most frustrating elo range to play in.
high elo doesnt get any better though. some high elo players spam op champs and many are very good at them. if u thought mid elo jayce players were annoying, try a high elo jayce who can actually aim well and knows what to build... it sucks
there are many champs that can stalemate vs jayce (ranged + sustain) but countering jayce is another story. u need a champion with more dashes then he has knockbacks . thats it. the problem with jayce is that whenever u engage, he will simply knock u back and do tons of dmg doing it. if u try to passive farm, he'll bombard u with EQ. u can either spend ur time dodging EQ, or u can spend ur time harassing inbetween his knockback cd. personally, i find more success with the latter. remember, jayce doesnt really have anything for a defensive cd or cc. all he has is his speed buff. if u have multiple dashes and some cc, u will kill him if u go aggressive.
think if jayce like AP nid. given enough free time and range, she will kill u. but if u get close, u can win.
a good champ to start with his renekton. his dashes/stun are great and he will win in a 1v1 duel if played right. diana also works but she's a bit harder since she's squishy at first and u need really good aim with Q.
diana bot is very simple, and yet still hard. theres no good way of saying this... either u dodge her Q or u lose. think of her like the old urgot bot. either u dodge his E or u lose.
now theres multiple ways of dodging. theres flat out moving away from them, which is hard (unless u can predict where/when she used her Q) or u can outrange them. now assuming u cant predict diana's every move, outranging becomes ur go-to option. think of a champ that ur good with that can farm from range (there r plenty) and have some form of defensive ability if u screw up. as u get better, u can start picking champs that can bully diana around
darius is easy. he's short range. if u get into his range, he will kill u. dont get into his range. its that simple. like diana, pick 1 of the many champs that have more range and u can win.
alternatively, u can bait out his ult and use a heal/shield to waste the cd. u may die anyway but a darius without his ult is a severely weakened darius.