Andrew, I can see your point. However a small diamond lead can give declarer an undeserved trick... Club lead = the same situation... So maybe a spade lead is safer after all...
How can East hope for game with his balanced hand, 7HCP and only three trumps? A clear pass! Maybe West can help him by bidding 2♥ instead of double, but the contract should stop here anyway...
A good example for what makes the difference between an average good player and a champion: the good player often settles for 3♦, but the champion will always bid 4♦. At home with no pressure at all almost everybody will say: "I will also bid 4♦!" But ...
Pretty reasonable bidding! I don't know if your 3NT bid shows exactly the SK or at least a similar to spade QJx stopper. Your partner can safely bid 4H with the HA in his hand, if he suspects that your pair hasn't at least two sure stoppers in ...
I ask myself the following question: "Can we play in 1NT if opposite there is a hand with 6 HCP and a small doubleton in our major?". If the answer is "YES", I pass 1NT, if the answer is "NO", I bid 2M.
Odds favor to bid trying to play in 3D. IMHO it's a very risky pass for penalty...Even if they raise to 3H I will pass and prefer to make they go down undoubled, instead of giving them an undeserved game.
2H doubled is oing to make 75% of the time. So pick 2S or 2NT (even they are not good bids...) just don't let they make the game by playing at the two level!
In my system I prefer to use 1x-2C as a GF relay and the rest of the bidding space is usually enough to identify the fit (even 4-4 in a minor) below the game level. Quantitative jump to 4NT is good if you will get to 6NT, otherwise I think ...
I use an easier to remember rule: " Don't bid the Grand Slam unless you estimate that three out of four you bid will make." This means 75%, but you will never be sure what are the exact odds until the end of the play and a safe reserve is ...
Partner didn't double 4C, nor 5H, so two suits are eliminated from the start. A spade lead might lose a trick in defense. So a diamond lead seems the only remaining option.