Manaless champs / energy champs

Would like some opinions on these types of champions (energy ones slightly less). Why are they allowed to exist? As far as I am aware; there is no distinct disadvantage to being manaless. The advantages of not having a resource associated with casting spells are actually quite immense:

**- You can spam abilities in lane to poke, without concern for running out of mana (Both no resource and energy).

• You don't run out of mana mid-fight, directly resulting in your death quite often (No resource only).
• You can leave the summoner platform after a back a good 2-3 seconds earlier (Health regens faster than mana. Applies to both no resource and energy). **

Just looking at faster returns to lane; manaless champs could be saving multiple minutes of time per game while not waiting for mana to regen. This may seem small, but it adds up. Over a game, that's more time to; farm, save turrets, get to objectives, clean up potential kills etc etc.

So again I ask: why do some champions get a free pass of all these issues?