Yeah, I het the NPC thing, but it is early game for the most part. Rando NPCs are actually good for early game to help show players strats and to help them when they aren't familiar yet with the system.
This is actually one thing I think Larian was quite clever about. If you notice, later, you don't get rando NPCs helping at all. It is your party alone facing most of the encounters.
One thing I will say about 4 party members that I do agree with, though I am a fan of 6. If you start with 6, and need to add a few more NPCs for stort purposes, suddenly, you have a REALLY big party. If you add 2 NPCs like Halsin or Sazza or whoever, and you have 4, your party becomes 6. If you add 2 NPCs to a party of 6, now it's 8. 8 is a pretty large party.
That said, they could, at that point, say that your party is full. In order to travel with an NPC, you must dismiss a member or 2.