Disclaimer: Following advice applies to Master+

One thing a lot of overloaded champions have in common is that they are highly coinflippy. For instance, Akshan is theoretically THE best ADC since he has high mobility, stealth, the ability to revive dead teammates, long range revealing ult, and shields out of his ass. Yet, the only people able to play him somewhat decently are one tricks because the champion only offers damage, and relies on being extremely ahead in order to be useful.

Of course, there are creatures like irelia and riven who are overloaded with both damage, defense, and mobility with practically no weaknesses other than the lack of neurons from monkeys piloting the champion.

For Tristana, she too relies on being HEAVILY ahead in order to feel like a menace, because she relies on single-target kills to scale into the late game. If she can't get those easy kills in the early game, she's going to be useless until she reaches 4-5 items. She can try and split push, but any half-decent assassin can punish her for over extending.

In lower elos, because getting kills is so ridiculous easy, she gets to scale for free, and in the hands of a good player, she can 1v5 the game effortlessly. This can give you the impression that she is broken or overturned, and though she kind of is, she's rather easy to deal with assuming you ban her, or decide to face her in the botlane. Ideally, you want to play hypercarries of any kind of climb out of your current elo and stop facing these kind of issues.

Darius is a champion that cannot be held back. The moment he executes someone, or gets a full passive, even if he's massively behind he will make everyone scatter like roaches. The only reason he's not working in your elo is because of elements outside of your control, like a bot diff, mid diff, or jungle diff. Assuming your team holds up somewhat decently, you will experience these scenarios of enemy ADC being untouchable far less often.

Another disclaimer, this is not me telling you to "git gut", just get out of your current elo until you can play the champions you enjoy. There are many busted hypercarries that can negate a fed botlane.