except this breaks the game because you can do BOTH for the same coast
So? That's meaningless. A healed party is a healed party. There is no reason to heal them once healed. The issue remains whether you can heal between battles or not - and you can. The restraint on the game remains the other limited resources available to the party. The battlemaster's run out of dice, the Warlock needs to recharge, the wizard has run out of spell slots, the bard is out of inspiration dice, the charged magic items are dangerously close to or at empty, the druid is out of shapechanges, etc.. Which, at least when I play, has always been the limitation on the day in 5e, even during the playtest. In fact I seem to recall during the playtest this was even moreso going on. This is how this version of the game is intended to operate. Nothing breaks. And I will note - nobody has reported a broken game.
all of the things you mention are applyable with or without this problem... and coast something...
Oh please, the Healer Feat costs charges of a healer kit, which is practically free. Far less costly than a 1st level spell, even one cast the day before (making it unusable if there is an ambush at night). And most of the rest of those are similar costs. The point is, healing between encounters is plentiful, and part of the game...not broken. I mean, when you've been playing the game, have you not been healing between encounters fairly often?
NOBODY has reported the game breaking from healing between encounters. All this is, is yet another way to do it. Big whoop. You go ahead and count out and save your little berries in a special cushioned basket, count each 4hp out, count each 24 hour period out, and track it all. Most people will choose another of the many methods of healing between encounters...one a bit less lame than berry accounting.
if you cast prayer of healing you use a spell slot that could be used for hold person or a damage spell or a buff spell to heal, with this cheat you can heal AND have the slot free for those things....
It's not a cheat. You making it a big issue without even bothering to ask if it's actually a problem for people's games. It's not. Notice the underwhelming reaction you're getting from people who play the game? It's just another method (one some people already used).
but what about after. If we end the day and I have a 2nd and a 3rd level spell left there is no reason not to just pop them for 10 berries at 5hp each and 10 at 6hp each... it isn't huge but it is more then any other combo can give.
Prayer of Healing currently does double that healing for those same spell slots. So does Aura of Vitality.