I'd expect the d throw tier list to be really weird, seeing as a lot of characters have good d throws. These characters' d throws are S-tier candidates, or at the very least could qualify for A-tier:
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. These are the characters whose d throws lead into rewarding combos and in some cases KO set-ups.
And here are the D-tier or F-tier throws, the ones that don't lead into combos reliably and can't score KO's well whether through set-ups or directly; many combos that are gotten off of these d throws are due to poor DI:
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Here the in-between d throws. Typically these throws lose their combo potential past lower percents, or are only useful as stock-caps:
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Meta Knight's down throw is a candidate for S-tier: decent damage (7.5%), has guaranteed follow-ups until ~80%, and can start KO combos on floatier characters. There are some neat things you can do with it, with d throw -> nado and d throw -> dash attack -> up air -> nair being simple ways of racking 25%+ damage. Then there are more complicated follow-ups like d throw -> PP FF bair, which can lead into upwards of 50%, and a potential KO. At mid-percents, if the opponent DI's in, they risk ~30% from an up air string. At mid-percents, there's a d throw -> PP bair killing 50/50.
The only thing holding back MK's d throw is that its high knockback growth (170), diagonal angle, and long animation (launches on frame 75) make it rather useless at kill percents against anyone who knows the MU. The diagonal angle, when combined with MK's mediocre air speed, also makes follow-ups difficult at the ledge if the opponent DI's away, down, or down-away, often limiting him to a fair follow-up, which is why ledge camping is quite effective against him. However, these issues shouldn't be enough to disqualify it from S-tier, especially considering several abusable d throws have been nerfed over time (Diddy, ZSS, Sheik, Luigi).