[pescetom]

Here is the full hand (second auction retained for clarity).

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 Gilithin, on 2021-October-09, 08:23, said:

Think about it - this is a forum question, not a random hand. For this to have made it here, North has ♠AKx and West heart length. We play the queen and draw 3 rounds of trumps, thus preventing ♥ ruffs. The trouble is that declarer should in this case just have started with the ruffs rather than drawing trumps. It's just a Grosvenor. I "know" this is the layout because there is a thread on the hand; in reality I am with Winston in playing low.

Yes and no.
Well done for spotting the layout, which of course had to be something unusual.
I don't agree that it's a Grosvenor Coup, FWIW. Here it is the declarer that acted illogically (as you yourself said) by trying to crash trumps rather than going for the ruffs, and while opponent putting up the Q is unexpected it results in defeating the contract where the alternative play of 6 does not. Also the reason why it worked will be clear to declarer and can hardly create a persistent state of doubt about any possible alternative plays.

 nige1, on 2021-October-09, 23:35, said:

"2nd-hand lo" is one of John Matheson's favourite mantras but see Gilithin's construction

That is the essence of my question: I would play low here, but is it just a mantra or is it good (or even bad) bridge?

 nige1, on 2021-October-09, 23:35, said:

IMO, the argument for playing the ♠Q is stronger, if the scoring method is imps rather than MPs

That was one thought I had too: at MP, not giving up a potential over-ruff may be more important than an off chance of defeating the contract.

Thanks to all who replied.

[Cyberyeti]

OK, so declarer played like a complete idiot in what is a laydown on normal breaks.