So I don't disagree with your first point, if you always play with the same teammate then it will be the best balance, unless one of you wants to play with another friend, or just queue up alone. But what if he is on holiday and you want your hit of TG enjoyment - arguably if you queue up knowing that you are underrated, you have become the smurf!Other than that, it's not only possible to game the system a little at the very top. Smurfing does occur very frequently, in my experience, on all levels on the ladder. While this will never fully eliminate smurfs, of course, it does make it harder to smurf unless all players on the smurf team decide to tank games, instead of just one. If this does indeed help combat smurfing to an extend, it does give a much smoother experience for casual players. Getting stomped by a team smurfing on the ladder is one of the more frustrating things in my opinion, and it wouldn't surprise me if more people get fatigued from this than from the scenario you described.
Basically, a more fair ladder overall makes for more balanced games, leading to a better experience for everyone.
In terms of smurfs I think I disagree. Imo it actually makes it easier to drop points - if a smurf wants to drop a 2k Elo account down to 1200, now he need to do is queue up with a friend on a clean/smurf account at 1k Elo, then resign after 5mins and instead of losing just 16 Elo (assuming a balanced match) I lose 30 (according to the aoe official example). This makes it much easier to drop Elo on a specific account and get to your desired range. The other option in terms of smurfing is just to make a lot of clean accounts and keep queuing up at a "starter" Elo, which is just as annoying, and there is no real control for.
I think that the only way to stop the smurfing is to ban the accounts reported for it. It's not difficult to see if someone queues up with the intent of dropping Elo and that would solve both the 4k Elo people after their ego hits and the smurfs who want to beat people worse than them on a lower level.