in a discussion of two versus three player games.

Well, to me, it seems like the need to hang back in El Grande is generated by the players. In other words, when the other players perceive that someone is winning in El Grande, they all gang up and rein him in. The punishment comes from the other players and is based on a perception, a perception that can often be wrong or motivated by meta-game factors like favoritism. Same goes for Alien Frontiers, which can even be worse because the take-that factor is high and scores are typically very close (i.e., within 1-2 points).

2. games that are mainly 2 player games but have rules for team games. A lot of war games are for 2 or 4 players, summoner wars is another example. The most popular multiplayer magic format is two headed giant which has people play in partnerships with decks that are designed to go together.

The most popular chess variant (maybe except for suicide chess) is bughouse chess where you and your partner play two games against a partnership side by side, If you are black, your partner is white and vise versa. In bughouse if you take one of your opponents pieces you give the piece you take to your partner who may use a turn to put it on his board.

I think the problem with 2 player war games that allow for 2 teams of 2 is that the game doesn't really change at all, and there's no hidden information between the two players, so it doesn't feel the same as a partnership game like Spades or Euchre or Bridge. In those, both players have to keep up their side of the partnership in order to win. If you're playing a 2 player game as teams, you can tell each other what to do, so it might as well be one player on each team.

Specifically, I want to comment on the idea that, to play games like Power Grid and El Grande, you have to hang back from the lead. Incidentally, this is a phenomenon that I also see in Alien Frontiers with more than two players. I've realized that I don't like El Grande, and to a certain extent, Alien Frontiers for just this reason. Unless I'm playing Diplomacy, or some other overtly political game, I don't want to have to hang back and worry about being picked on because the others think I'm winning. As a result, the responsible gamer in me must confront the question: Why do I enjoy and defend Power Grid when it has a similar feature?

When you called Mark the grandfather of boardgame podcasting though, I couldn't help of thinking of Aldie and Dirk. Wasn't Geekspeak a.k.a. Boardgamespeak first? (Or did I just discover it first?)

I think people that like Euros should not be so afraid to try two player direct conflict games. Direct conflict in two player games can be much more satisfying than it can in a multiplayer games. I really think they are entirely different experiences. In a two player game there is no viscious or petty actions available. However, in a (flawed?) multiplayer game with direct conflict, there can sometimes be ample opportunity to "Kingmake" or illogically "hose" another player.

I've never felt the need to hold back while playing Settlers

That's it. While it's true that the leader in Settlers finds himself the victim of every robber and rarely gets to make a trade, that's not enough reason (in my experience) to play a sub-optimal game at the midpoint. Whereas in El Grande it feels to me that's exactly what you need to do.

Just an aside:

I think it's important to be clear about our terms. Playing "optimally" and "sub-optimally" is going to vary by game. In a game where appearing to be in the lead is a danger, it is an optimal move to hold back. Let's not confuse the issue by saying that, in order to do well, you have to play "sub-optimally" by holding back in such games. Holding back is not playing sub-optimally.

It comes down to personal preference as to whether you enjoy games that require holding back (or "positioning yourself" or whatever).