Why some champions are allowed to be completely resourceless?

I am specifically talking of those champions:

They all share one thing in common: to cast a spell, they literally don't have any cost, with the sole exception of Shyvana's ult, which requires her to have full fury bar.

Do you realize that all of those champions are, or have been unbalanced? All of them were nerfed, and some of them are still very powerful. All of them are or were constantly complained about. And on my opinion for good reason.

Why those champions are allowed to cast their spells completely freely? The only real limitation to those spells are their cooldowns, but this can be mitigated by stacking cooldown reduction. Although many of them already have low cooldown abilities. Katarina in particular, actually has a cooldown reset on her passive. This actually allows her to forgo purchasing cooldown reduction items, which open possibilities for her to build strong raw AP items such as Luden's Echo or Liandry's Torment. There is also Yasuo: his Q's cooldown scales with attack speed, which is one of his core stats, while his Q can be cast instantly on any target as long as it isn't the same target.

Meanwhile, other champions are forced to waste precious resources to cast their spells. This limits the ability to fight with those champions, who can potentially outsustain any champion that is limited by mana. For example, even though and are, in theory, counters to Riven and Yasuo, respectively, they are severely limited by their mana pool. Because of this, they can't play nearly as aggressively because otherwise they become OOM. If Malzahar wasn't limited by mana, he could actually counter Yasuo by constantly using his E on Yasuo and by outpushing him. But in actual play, if Malzahar tries to do that, he will become out of mana before actually being able to force Yasuo out of lane. Same thing with Malphite. If he wasn't limited by mana, he could harass Riven with his Q. Instead, he is forced to wait for Riven to engage and use his E to trade with her and reduce her damage potential.

I would like to know what those champions trade for their ability to cast spells. Because they don't have any actual resource, and as I said above, they are only limited by their cooldowns. Notice that some of them (Riven, Katarina, Gnar, Yasuo) have low base health regeneration. However, all of them can buy sustain items to mitigate this, with the arguably exception of Katarina, but she can still buy a Hextech Gunblade if she wants sustain. Most of time, however, she will just burst you down before you are able to sustain against her damage.

I would like to know why it is fair that those champions have outstanding mobility too, meanwhile champions like are completely immobile and are still limited by a mana bar.

EDIT: I didn't listed champions like , , and because energy is still a resource that they have to manage and a Zed can potentially go out of energy before being able to unleash his full combo, while champions like Vladimir have health costs, which are actually worse even than mana costs because it leaves them extremely vulnerable, and forces them to buy sustain items to mitigate those costs.