Having a healer is a rediculous advantage to not having one, or only having Reyna or Kleese (which I think Kleese is underrated, but that’s a discussion for another day). Let’s break this down into 3 scenarios:
Scenario 1 (You Have No Healer) - Your team is pushing minions, lightly skirmishing over the center map’s objectives (the turret, the crystals, or the mercenaries), and taking a combination of both minion damage and player damage. Your shield is good for mitigating some of the poke and minion damage inflicted on you, but if you sustain any heavy damage, it will begin to be inflicted on your health. Now you are in a heated fight, and you manage to escape with 1/4 of your health. You now have to make a decission, do you wait for your shield to recharge, and return to the lane, or do you go back to restore your health. If you decide to go back into the lane again, you are at a very high risk of getting killed, either by a sniper, or by a smart player who exploits your weakened state, and if you die, you now suffer a HUGE punishment of a respawn timer, feeding your enemy XP, and the walk back to lane once you respawn. That respawn timer, and the walk back means you are depriving yourself of XP and shards, and depriving your team of momentum, and ability to defend or contest objectives. If you decide to go back, you still suffer the penalty of running back into lane, which has the same negative effects on your team as dying would, but not as long. Either one you choose, you are at a loss at this point.
Scenario 2 (You have a shield support) - Having a shield support is nice, because you can mitigate more damage in combat, meaning you will sustain in lane for a longer period of time, but what happens when you, again, escape a fight with 1/4 of your health. Sure, a Reyna overshield will help mitigate an extra 400 damage if you decide not to go back to base, but ultimately you are still at the same disadvantage as you were in the first scenario, but you now have 400 extra shield to play with, meaning you lower your risk of death. Not as bad, but a smart player will still realize your disadvantage and exploit it, by forcing a fight you can’t win. The point is, shields are nice to mitigate damage, but it doesn’t solve the main issue of the 3/4 of health you are missing, which is the bulk of your survivability. You are still in the same predicament as before, and will still suffer the same penalties if you either die, or go back.
Scenario 3 (You have a healer) - Just like in the previous 2 scenarios, you manage to escape with 1/4 of your health. You and your healer disengage to some cover, and they quickly heal you back to full, while your shields recharge as well. At worst, you take cover behind the sniper’s nest, and deny a wave of minions for you and your healer. At best, you take cover close to the action, and manage to heal up while providing decent aggression at a safe distance. Either way, you are only our of the fight for about 10 seconds, before you are ready to go back into the battle, and continue the push. In combat, your healer is just as good as a shield support in mitigating damage you sustain, but they are also able to help you quickly recover if the fight turns south. You won’t have to go back as long as your healer has half a brain, thus never having to suffer the penalties of going back to base, or putting yourself at a disadvantage for your enemy to exploit, and risk death.
As you can see, the benefit of having a healer is undeniably better than the other 2 scenarios. The longer your team can stay in lane, the more aggression you will put on the enemy. The more aggression will lead to harder pushes. Harder pushes lead to more damage on the sentries and more XP for your team. More XP makes you more powerful. Being more powerful helps you snowball. This game already has some issues with snowballing, so if you don’t have to give up your momentum, why would you? Like I said before, even if you nerfed their healing to the ground, it would still be quicker than going to base. Some may argue that in casual play, your healer might not heal you, or your enemy might not be smart enough to exploit your disadvantages. But with that logic, you could effectively argue that all strategy is meaningless at that point. If you are playing at that level of casual play, then this problem shouldn’t affect you anyway. But if you are playing anything more than a casual level, having a dedicated healer is a MUST.