So about potions replacing spellcasters- let's examine this more closely. I'll look at the arguments in no particular order.
1: why use healing spells if potions are more efficient?
But are they though? 50 gp to get an average of 7 hit points restored. That's worse than a Healing Word in 2024 and has an opportunity cost at low levels when coin really matters. It also assumes plentiful downtime or ready access to somewhere that has potions for sale- not something you can assume in the field. I'll touch more on availability later, but this amount of healing is a drop in the bucket. The better healing potions will eventually become better at healing than cure wounds, but come with even higher price tags.
Also, consider the difficulty of getting your healing spell to the target when they need it. It's far easier on the Cleric if everyone has their own way to heal in case of being locked down by foes, or unable to get to injured party members.
2: why cast buff spells if you can buy potions?
Now maybe someone else has seen this work out differently, but my experience has been that most buff spells are just not efficient enough. If it takes concentration, then generally a spellcaster has other, better uses for it. What's more efficient, casting Haste on the Fighter, or using Hypnotic Pattern or Sleet Storm to lock down multiple foes? Even Slow, which is less efficient (smaller potential pool of targets, repeated saves, nerfs, does not stop enemies in their tracks), is probably better than giving your martial one additional attack. The days when I could reliably get some kind of concentration buff for my melee character are long gone.
3: potions save spell slots.
Even if this is a problem, the same issue occurs with scrolls.
Next, you have the argument of availability. Do the players have the means to actually load up on tons of potions to make this a problem? Healing potions are in the PHB. Other potions are treated less as equipment and more like other items. Can you get the potions you need/want? If the party needs, say, 10 potions of water breathing to explore a sunken ruin, how easily can they acquire them?
Finally, there's the thing everyone keeps skimming over. Bonus actions in combat. Many characters have other things they want to use these for, and designers keep overloading the bonus action. A Fighter might have a bonus action attack from a Feat or subclass. Their Second Wind definitely requires a bonus action. A Rogue might need their bonus action for hiding, escaping, or aiming. A Barbarian needs their bonus action to rage. Monks need their bonus action for flurry of blows or dodging. Want to apply that Hex or Hunter's Mark? Activate that Smite spell? Even casters might find themselves in this situation, like a Sorcerer wanting to Quicken a spell or a Wizard needing to Misty Step out of danger. A Cleric might want to use Spiritual Weapon (though perhaps less often than they did in 2014).
Not every character has a use for their bonus action, but many do. If this is the case, using their bonus action for a potion is better than using their action, to be sure, but they might be loath to do so if it hinders them "doing the thing" they want their character to do.
And even if somehow potions step on casters...so what? Wouldn't that be true of many magic items? I have a +2 sword, who needs Magic Weapon? Boots of Speed, Broom of Flying, Robe of Eyes, Helm of Comprehending Languages, Ring of Invisibility- if it's not boosting numbers, it's granting someone an ability that otherwise requires a spell to use.
And that's not even getting into the fact that having a spellcaster shouldn't be required to play the game! Niche protection is mostly dead (or is supposed to be), isn't it? Why not let people get by without having a dedicated magic user in the party?