Valve employees can do the core gameplay design and art, and they can hire other studios to help out.

thats a great way to make a double A 70~ish metacritic game 

I accepted that it will never happen a long time ago.

It's hard, but that's all you can do, honestly.

big studios are much bigger than valve. we can simply expect most people at valve to be unavailable for main game development. that leaves ~100 people. thats like 1/3rd the baseline imo 

Do they even want to make AAA games ? Valve is both dead to me as a game publisher/developer and as a digital retailer ...

That's exactly how lame they are ...

No. Half the team left the company, including the series story writer, Marc Laidlaw. 

Even if they did, they don't have the desire to do it, and why would they when they can just sit on mountains of cash selling other people's games on Steam?

If you think HL3 is or will ever happen, I've got a bridge in Brooklyn I'd like to sell to you.

Like Uncharted and stuff, yeah.
You don't need to hire hundreds of employees to do grunt work when you can just outsource it.

ND is over 250 and they have the visual arts team in santa monica which is basically their studio thats also ~50+ people. 

I'd rather see a sequel of Doom 2016, best single player FPS gameplay since Halo.

we're talking about a triple A game here

HL2 took 6 years. this is 2018