It seems like if you have invisibility you are automatically a strong champion by default

Well, yeah, kind of. But that's because invisibility is a strong thing, especially when it's those in-combat stealths that can only be broken with Truesight.

To sort of visualize it, imagine their kits as being something of a finite energy resource that all gets distributed to them. I'm going to take Kha'Zix for this example, but do try to apply it to the others.

Let's start at 100% now, let's look at his ult, giving him two bursts of invisibility that he can only be revealed from through damage shimmers and Truesight. So, only specific champions have Truesight, meaning he has a limited champion pool who can counter it through that means, so the most ideal way to reveal him would be damage shimmer. Let's say that that takes about...35% of his power budget, since, when upgraded, he passively gains that invisibility when stepping into brush.

65%.

And now his Passive, which causes him to do bonus damage when he's unseen. That'd take up an extra 15% of his power budget, since it goes hand-in-hand with his invisibility.

50%.

Then his W, which is a line skillshot that does AoE damage and heals him if he's in the AoE, which, when upgraded, becomes three skillshots in a cone, same functionality, but they also slow. 20%.

30%.

Now his Q, which deals damage and has increased damage if the target is isolated. When upgraded, his basic attacks and Q both have increased range, and if he Q's an isolated target, it refunds 60% of the cooldown. 20%.

10%.

And, lastly, his E, which is a short-range jump that, when upgraded, increases range and has cooldown reset on kill. 10%.

0%, all resources spent.

Now, I'm not exactly the best judge of power with abilities, but I say with confidence that I'm sure these'd be the correct percentages to these abilities. And, other champions' ability power budgets would no doubt differ, but exclusive to Kha'Zix, I feel that his strength comes both from his invisibility, and the balance of power with his upgraded abilities.

And of course, the differences between Champions and their abilities also opens more room for discussion on how their power budgeting is in relation to their abilities and, consequently, their stealth mechanics. Just keep in mind that stealth mechanics will undoubtly, across most if not all discussions, be attributed with a large chunk of the power budget when it's brought up.

no rengar?

?