Yeah, that's true, though part of it is likely due to his lack of safety. Unlike carries like Graves, Vayne and Ezreal, Kog'maw doesn't have a direct escape. Unlike Ashe, Varus and Draven, he doesn't have hard CC to help him escape. He's fantastic when positioned properly, but he's easily destroyed out of position.
Ezreal has two main advantages. The first is his passive, giving him a +50% AS steroid as long as he keeps hitting people with spells. The second is his Q, which is a spammable spell that does everything but crit like a normal auto attack.

He's one of the carries I think of as all-round in game scaling. Unlike Caitlyn, who has fantastic early and then a (relative to carries) weak late game, or like Kog'maw, who has a weak (even by carries' standards) early game for a fantastic late game, Ezreal is one that holds the same level of effectiveness from level 3 to 18.

I think people are scared of her, they've heard shes a hard carry and they play the weak melee carries because they're cool in some way and "hard carries" and then they're like ok hard carries suck

Or they play vayne or kog'maw and go ok even these ranged hard carries suck, because they're hard to play.

Out of all of the hard carries I think Trist is the most feasible for joe blow to play and do great with.

Trist is great as ADC. She has such great range and such a great AS steroid along with good ways of escaping which make her do huge amounts of damage late game because she can itemize less defense than many other ADs which allows her to itemize more damage.

Caitlyn also has a much stronger lategame than people seem to credit her for because of her safety. She, like Tristana, is able to stay alive more easily than most other ADCs which allows her to output huge amounts of damage.

edit:
in short; people really underestimate the advantage that huge range gives Cait, Trist, Kog, and to a lesser degree Ashe. Its also part of hte reason Ez's Q is such a phenomenal spell, its like an extra strong autoattack but with huge range

She is weak atm, but she is getting a pretty substantial buff pretty soon along with Vayne and Ashe.

How much will the ads buff affect them?...

50% AS passive and a team buff to boot.

trist has a rather profound weakness in that she cant exert pressure outside her attack range. in the late game that's fine, she can shoot you from a mile away. in lane that means trading every single time and being rather obvious about it.

For 5x5 She suffer a bit with subpar range early and pushing tendency.
I'd still send her mid like in old times. (She can build AP, hybrid or on-hit if oyu are concerned about trading with a mage)

they are getting buffs to their attack speed per level which is quite a strong buff for ADCs.

vanye: 3.1% to 4.5% per level
trist: 3.01% to 4.5% per level
ashe: 3.1% to 4% per level

Isn't there a way to turn off her "E"?

My favorite ADC in the past has been Miss Fortune for her crazy strong early game, and excellent AoE team fight damage. She is also extremely good at chasing down kills with strut and her Q.

However, lately I have been playing Tristana again and she is still an amazing carry. Lategame it's pretty unquestioned that she has one of the best carry potentials, but her early game is also very strong compared to other ADC, assuming you prioritize W and E for spell leveling.

She is definitely not a strong poke champ in early game in the traditional sense. You can try exchanging pokes with her E, but it is usually a waste of mana. Her autoattack range is fairly average at the start of the game, so you will be taking auto attack hits and buckshots/etc often and you will generally lose the exchange if you try to out poke them.

However, if you put all your points into W and E without any in Q, your early game burst is crazy good. If your support can land a CC on their carry, you can generally jump in + E + ignite and it will be an easy kill, with a chance to get their support too because of the refreshed jump's slow.

As others have said, her one weird point is transitioning from early to late game, where your burst from WE is not enough to kill and your autoattack damage isn't amazing yet. Getting an early game lead is pretty easy, so this usually isn't too bad, but it can be rough when matches are slow farm fests when you hit mid game.

Some useful tips that I live by:
1) Max WE without any points in Q is best until you get your IE, then put all points into Q to dominate early game and then a quicker transition to late game, usually this will leave you with maxed W and 2 points in E before you start maxing Q.

2) In team fights later, just autoattack and save R for a melee that is on your face, and jumps to get to keep some distance (even against other ranged this can be very useful since you outrange most). Once a few of them die, then it is generally safe to rocket jump into the fray.

3) Standard ADC build/runes/masteries work well on her. BUT I actually prefer masteries of 9/0/21. Starting with a doran's blade and a health pot and a biscuit is very useful when they want to trade pokes. The utility tree is surprisingly potent this season, and the extra movespeed, lifesteal, CD, experience, and gold generation from pickpocket and greed are all much more useful to me than the bit of extra damage in the offense tree.