The issue is that I feel like there is not much reason to bring a person around other than for their fighting skills. As soon as the fight is over the companions will cease to exists, other than the occasional utility spell thrown around.
As you said, having an expert around. My grumpy monk should be smart enough to say "wyll, talk with these guards or I'm going to talk with my fists". If I'm in a magical dungeon with magical writings and magical stuff around, I'd like to bring gale to be helped to understand what's happening.
Each conversation is lead by the character that initiates it, and only that character gets to speak via dialogue options. Other companions occasionally interject with their opinions, receive approval/disapproval depending on your choices or grant an optional bonus to skill checks if they have spells like Guidance or Charm Person, but they won't be able to switch places with the active speaker or handle any checks for them. If you want Wyll to persuade the guards instead of your Tav, you'll have to select him and have him initiate the interaction. Strangely enough, Wyll speaking and making decisions can still generate approval or disapproval for your Tav, but (someone correct me if I'm wrong on this) not from Wyll himself. Also, if Wyll would normally have a unique comment on your conversation with the guards, you won't see it.
As for non-conversational skill checks, companions are worth having. The world is littered with skill check prompts such as Perception checks when walking past buried treasure, Arcana/Religion/History/Nature checks upon spotting a strange idol or an unusual plant, as well as Medicine/Investigation checks triggered by a corpse with identifiable wounds. Each companion rolls their check separately when approaching the prompt and a single success is all you need, which makes having a party of 4 with a diverse skill spread valuable (at least for these interactions).
