As a player of uncommon systems (weak NT in a very strong NT environment, Strong Club systems in a standard/2 over 1 world) I agree with Alexander Woo (who likely won't be surprised). However, variance is actually a very interesting topic at matchpoints.
Possibly the hardest part of matchpoints is working out what the contract really is when dummy comes down (and on defence, it's even harder). 120 vs 90, or 430 vs 420, is the same matchpoint as 1700 vs 620. Say the auction ended at 3NT. But when dummy comes down, you realize that everyone's in 4H, and it's making. So now you have to make 4NT, because 3NT= scores (almost) the same as 3NT-1. Or you notice that if they had led a diamond instead of a heart, 3NT will go down; so now just taking 9 tricks, even if you have a chance for more, beats all the tables that got that diamond lead. Or you realize that everyone's in 3NT, and everyone's making it, and it's a fight over the 10th and 11th trick for the matchpoints.
Variance, or "not going with the field", makes this harder, whether it's "in the room, partner is playing 3NT, did we get a good or a bad lead as a result?" or "our weak 1NT opener likely stopped them from bidding hearts, what does that mean?" or "our auction went 1NT-AP, the room is bidding 1D-1S; 2S - how many NT do I have to make to beat the players in spades?"
Variance is not necessarily good or bad; unless it's clearly inferior or superior, it doesn't change your mean score. What it does is increase the deviation, and with each board in a 25-board session being worth 4% of your score, it can be a lot of increase! When you get the day where your system means you're in 5 bad contracts, that no matter how well you play them are going to score badly, it doesn't matter if you're a 60% player in the field - you're still not breaking average. When you get the day where your system nets you 5 good contracts (over the field), though, your 45% game becomes a 58% and you might win.
I played Precision at a National level (not that I am National level, but we liked the challenge!) for 5 years. The worst thing bar none, the times that caused the grey hairs, was when I knew the standard bidders were having a mindless "book" auction like 1NT-3NT, but our unusual auction showed us that the "book" contract was bad. Do I back my system, knowing that 30% of the time the "bad" contract is right and I get a zero, and even when it's wrong, some will bring it home anyway and beat me; or do I go with the field knowing that 70% of the time it's a bad contract (and I'm not as likely to bring it home anyway as the National level players)? Or worse, I'm at 3H, and I know there's a good chance at 6C, but if I go looking, I can't stop in NT any more. I know the "book" auction won't find out about the slam potential, and they'll all be in 3NT. I know that 3NT+1 (which likely will happen) beats 5C, or even 5C+1 when they don't find the setting lead to 6. Do I try? Or do I just bid 3NT with everyone else and "try to win the board in the play"?
On the other side, there's a strategy. "Get to the field contract, and beat them in the play." This is a low-variance strategy, and it works. For the better card players in the field, minimizing variance in the auction - which, yes, includes "bidding bad games" that everyone else will bid - gives you field protection. Your "bad contracts" will be 40% or so, not near-zeroes, and you still have a good chance at 65% if you play them one trick better than the field, even if it's -1 instead of -2.
But of course, for this to work, you actually do have to "beat them in the play". If you're not the "better card players" in the field, then turning 5 or so of the 25 boards in a session into crapshoots means that on the day when they all go bad, sure your 45% becomes a 38%. But when 4/5 of them work, that same 45% game is a 54, 55% game (frequently at the expense of the best players!)
As Alexander Woo says, many of the readers of bridge advice - and almost all the writers - are "better players" in the field. So you would expect to see this strategy. As I said, it's not wrong, for them!
What I will agree with the "strategy" people is "the best use of your time improving your game (in general) is play and defence. It's not as much fun as playing with system, but it pays off more." It doesn't matter if you're the best bidder in the world with the best system in the country if you can't make the great contracts you're in because you're only an average player. And as everyone is discussing here, if you're one of the best players in the room, almost every hand has possibilities to get ahead of the field - even if you bid as badly as the rest of the field.
The question of course is then "why play a high-variance system at matchpoints?" Well, frankly, most don't - they play the system they learned, basic or sophisticated as it comes, which is the same system almost everyone else plays. This is even more so in the ACBL (the Hamilton Bridge Club is in the ACBL) than in other parts of the world. Those that do:
- it's the system they learned (in England, or Poland, or China, but now playing in Hamilton);
- It's a system they're comfortable with (I just find 70% of auctions in a weak NT system easier than in standard) or better suited to their mental states (Strong club systems like Precision frequently are much more detailed than standard, so you're "on book" for longer before you have to use judgement; the cost being more memorization. I'm someone who can memorize long series of tables - or recreate them from rules on the fly, sometimes - so for me, it's a win. Most find this a tax on their memory, and are worse off).
- it's fun to be weird, and present an unusual challenge to your opponents. And most players, even the "better players", play bridge to have fun. It's not like poker, where loose play costs actual cash.
- they're tired of "normal" and just want to do something different sometimes (note that there are people who are exactly the opposite and "something different" is way too tiring!)
- they're in a game where "second place is the first loser" and they're unlikely to win playing straight up. Playing high-variance, they will likely do worse - but when everything goes right, they get 10% "for free" and their 52% average is a 62% win.