I just had a discussion with a friend who asked me to explain why I think the titular conventions are some of the most overrated systems in bridge, and it seemed worth briefly writing up. To be clear, I'm talking about systems where after the opponents have opened 1NT, 2M shows 5major, 4(+) minor, and you use 2C or 2D to show (both majors) and (a long suit, possibly explicitly a long major suit) either way around.
Looking at the the overcalls in ascending order:
X
This is not integral to these systems, so you can play it however you like. No problem here.
2C showing both majors
I like this use of the bid a lot. I think vanilla Landy is a very good system.
2C showing a long suit
Fine, I guess. No strong views, except that it takes away your 2C-both-majors bid.
2D showing both majors
This is ok, but losing the ability to have partner bid a forcing 2D 'no preference and/or tell me more' means you have to overcall more conservatively, and occasionally makes it hard to find your games.
2D showing a 6-card major
This has many ugly properties:
- By making a (nearly) entirely forcing bid, you're giving prepared opposition free double, as well as a free pass-then-bid which gives them a tonne of extra room to figure out eg how strong they are by playing X as values, and occasionally saves them from 'competing' in overcaller's suit.
- By specifying that the suit is 6-cards, you're helping partner but also the opponents know when to compete, and I contend that the latter is the more important factor, since it's right to bid 3-over-2 much more often than it's right to bid 3-over-3.
- Lastly and leastly, when the hand is played in 2S (after 1N 2D P 2H / P 2S P), you've helped the opponents defend by telling them declarer has the extra trump, and when it's played in 2H (after 1N 2D P 2H / P ), you've put the strong hand on lead, which is a slight upside, but your partnership also has its likely stronger hand as dummy, which is at least a big a downside.
2D showing an unspecified 6-card suit
This has a slight advantage over the major-promising version in making the auction 1N 2D X P / P a live possibility - ie your values double could end with you defending 2Dx in an 8-card fit or worse. Other than that I don't have any concrete arguments against this, but my instinct is that overall, a constructive overcall is less useful the less it tells partner about your hand.
2M showing 5M, 4(+)m
This is the real disaster of the system, despite being its main purpose. The problem is a) that you can't be confident P has your minor, so you'll often miss a good fit when you have one, b) that adding an extra card to your trump fit gives your side substantially less than an extra trick in expectation (let's say it gives you 0.75 extra tricks for the sake of argument), and c) that you've the opposition exactly how to play/defend the hand.
Keeping a) and b) in mind, here are a bunch of bread and butter shapes you might expect to have opposite a 2S overcaller on which you'll usually want to pass:
3442, 3244, 3424, 2443, 2434, 2533, 2353, 2335, 1534, 1543, 1453, 1435, 3334, 3433, 3343, 2542, 2524, 2344(!), 2245(!!), 2254(!!)
The last three really show how ridiculous this system is - you have a guaranteed better fit available in a minor, but because the most likely fit is only one card better, by bidding on you'd still be reducing the overall probability you make your contract. So on all of these shapes, you've needlessly given the opposition vital information on whether they should stay out of the auction, compete or defend, and how to play the hand either way. For it to be worth competing at IMPs, you really need 3 cards more in both minors than in your major suit - ie shapes that are absurdly improbable in comparison, like 1444, 1345, 1354, 1255 etc. At MPs you might still pass the first three if you have enough values that you expect to make.
In the abstract, the weaker advancer is, the more appealing it is to bid on, since you're unlikely to make a 7-card fit on power, and the chance of a 9-card fit might be a gamble worth taking. The trouble with this reasoning is, if you use 2N as a forcing minor-asking bid and primarily do it when weak then, as per the previous sections, you've given the opponents a free double or pass-then-bid, giving them ample room to penalise you when you land in your more likely 7-or-8-card fit, and to compete or even find game otherwise. You could use 3C as pass or correct, which is probably better, but still gives up what might be a useful bid.
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