The healer feat's healing is equivalent to a cure spell at the following levels:
Cure 1st (9.5) - level 2
Cure 2nd (14) - level 6-7
Cure 3rd (18.5) - level 11
Cure 4th (23) - level 15-16
Cure 5th (27.5) - level 20
So the Healer Feat is worth a lvl 1 Cure Wounds at lvl 2? And isn't worth a 5th lvl Cure Wounds until lvl 20?
I suppose your point is that the Healer Feat can do it once to every party member, though a Healer Kit only has so many uses. I guess it isn't that expensive, but still. A Party of Five can only use it for two days before it's used up. Cure Wounds can be cast as long as there are spell slots, which continue to regenerate every long rest (or short rest for Warlocks). But I think it's not fair to compare a skill at 20th lvl to a 1st lvl spell that's been upcast with a 5th lvl slot. A first lvl spell will never equal a 5th lvl spell, and Mass Cure Wounds is a 5th lvl spell that can heal 3d8+Mod to six people. I'm not sure about averages, but going by your chart there, that's an average of 18.5 to six different people with a single spell, at character lvl 9. Healer Feat at lvl 9 can heal 1d6+13, which is between 14 and 19 hp, to a single person per use. It would use up 6/10 uses to heal the same number, for likely fewer HP. And they're using money to "cast" it instead of spell points, because they have to buy the kit.
Nobody would ever use Cure Wounds in a 5th lvl spell slot unless they knew they weren't going to need that 5th lvl spell slot. Cure Wounds is ok for lower lvl healing, but at higher levels it's basically a "You're dying or unconscious, let me get you back up and in the game real quick". At higher lvls, there are other things you can use.
You need to compare lvl to lvl, not a lvl 5 spell to a lvl 20 ability, and certainly not a 1st lvl spell upcast with a 5th lvl slot to a lvl 20 ability. At lvl 20, you can cast Mass Heal, which doe 700 hp worth of healing. Per day. No gold spent. If you have 10 party members, which very few parties have that many, you'll go through an entire Healing Kit and heal, if your average is right, 275 hp total.
So yeah, healer can make you an effective healer, if you're willing to carry around a bunch of healing kits, and will outstrip Cure Wounds after lvl 6, but to be honest, if it didn't outstrip a lvl 1 spell by lvl 6 then it would be useless and nobody would get it. A Cleric or Druid will always be a better healer because they get better healing spells as they get higher level.
I just looked up Regenerate. 4d8+15 and then 1hp every six seconds for an hour, no concentration. 10 hp per minute is 600 hp, plus the initial healing. At lvl 13. My goodness, throw taht on the tank and let him solo the BBEG! He'd never die! Even if he went below 0 hp every round, he'd get up at the beginning of every turn! So yeah, having a healing caster is much better than just the Healer Feat. I don't see how Healer is at all over powered.