Posters here seem to agree that PCs should be more powerful than ordinary folk in a typical campaign world. So I don't think it is right to raise the spectre of wanting them to be "more casual people". Rather I think the concern is - how reliably should PC skill checks (active, passive or contest) defeat monster capabilities? With that in mind, I'd want to give skills to monsters, before I changed Expertise or nerfed optimal builds.
A wolf gives a good idea how well this plays out. It has proficiency in perception and gets advantage on top of that, whenever relying on hearing or smell. A ranger with proficiency in stealth and prioritising Dex (say +4?) at level 4 might have +6. Stack in Pass Without Trace (2nd level spell, +10), and the wolf might (rarely) still detect the ranger. Stack in Guidance or Bardic Inspiration and the wolf might be unable to detect the ranger. Still, this is a CR 1/4 monster and the party have thrown in a few resources.
On the other hand, most creatures don't have proficiency in a wide range of skills that to me feel as if they should be common - such as athletics - far less advantage with them! So you can see how without proficiency a party can just perma-beat many creatures, even in tier 1.