Neither of them are a 100% true.
The earning rate of US Platinum Card is 1 MR point per USD whereas the Indian Platinum Card earns 1 MR point per Rs. 40. (That's 2 MR Points per ~$1. US Platinum Card has 1:1 Conversion ratio whereas Indian Platinum Card has 2:1 conversion ratio. So effectively, no difference in Airmiles accumulation. The loss is in Marriott Bonvoy.
The major difference is the Airmiles Partners on the Indian Platinum Card Vs the US Platinum Card.
Zero Forex Mark-up - This look lucrative but the conversion rate and remittance charges while sending money into US Bank account for paying the US Platinum Card Bill is a decent amount taking away any major benefit of the Zero Forex Mark-up.