For what it's worth, as an Ambassador, I checked in to Le Meridien Bangkok a week ago for 14 nights and I received an upgrade to a suite. I'm surprised to learn that the hotel is full, the lounge has been all but empty in the afternoons and likewise the pool is empty most of the day too. I sat alone in the lounge for over an hour yesterday, not so much as a peep from another guest. I did see a large tour bus outside a couple of days back and maybe that has contributed, but overall, I'm not sure if the hotel being sold out on Tuesday is representative, it doesn't feel close to capacity.

All that isn't to say you're wrong, if the front desk said it's at capacity then I'm sure it's at capacity, but it certainly feels like low season to me. I am having a great experience here and attributed it to, in part, the low season: if this is how the hotel operates at capacity, it is one of the best run hotels I've ever stayed at! Perhaps some rooms are out of service for some reason? An alternative explanation is that they've priced the hotel very competitively in order to achieve high occupancy in low season: I'm paying just 4,900 THB per night which makes it one of the lowest price Marriott hotels available in Bangkok.