That's what we did before transferring to Conrad and I don't regret doing that due to our long flights/layover from NY to MLE via Dubai. For Sheraton, at least you know you will get to the resort promptly via boat once you arrive at MLE. We were so tired on arrival, we slept pretty much all day and night so the lesser cost of Sheraton kind of makes it the right choice for the first day or two.

For seaplane, they only let you know the time of your flight the day before. So you have the risk of waiting many more hours after your long international flight(s) to get to W via seaplane. If you consider Sheraton just as a transfer hotel and don't set high expectations, it is a fine property. Plus you will appreciate W a lot more after staying at Sheraton.