mastercoms

You forgot to mention contracts as well

The player closest to the average MMR needed to balance the skill level of both teams is preferred.

I think the problem here as I've explained in the past, is that matchmaking is a much more general term than skill-based matchmaking, and even that can come in many different forms. But, like you said, we pretty much agree on what should be done for the most part.

Just like autobalance is supported, team switching and team scramble can easily be supported even with slot reservations.

As for spectate mode, it'll take a little bit more work for that, but they removed that because it allowed players to dodge certain votes at the time. I think it's been fixed and they should add it back, though it requires a little bit more work since slot reservations are only aware of the RED and BLU teams.

Ad-hoc connections can easily be supported even with slot reservations.

None of these features are blocked necessarily by slot reservations. It's just that when they were developing slot reservations, they had none of these features in mind, so they weren't a priority to add to the slot reservation system. As we saw with autobalance, things can be made to work with / be aware of the slot reservation system.

And, this doesn't really necessitate the removal of skill based matching, though it would require some work. Personally, I think players filled with noobs should be protected from joins (ad-hoc disabled). And then otherwise, the GC should be made aware of the skill of people coming in through ad-hoc joins / the balance of teams in team scramble (team scramble can be informed by skill rating as well, just like autobalance is, btw). Then it can make adjustments to balance out things as needed through more late joins, or shuffling the teams after the match ends.

Most of these things are a few lines of code. It's not much work for Valve to do, and the fact they haven't done it just means their goals/priorities were different, not that somehow that slot reservations conflict with these settings.

And to reiterate, my personal view on this which I've shared in the past is that while slot reservation on teams is a pretty noble idea, it should just be a slot reservation into the server, and then dynamically balance teams as players join in. Because in practice, slot reservations per team, just means lots of people can get loaded up on one team and create imbalanced matches, and makes autobalance less responsive.