I've stayed at the Edinburgh Marriott for about the past 6 months also on business (as the hotel is right next to a large business park where my client is based) and fully agree with your assessment. The hotel is regularly sold out with coach parties which is their main source of revenue along with business travellers which pushes their rates much higher than they should otherwise be for the quality of hotel. The staff are also so-so (a few good members) - I think the best part is actually the head chef who does a new specials menu every 2 weeks with ~3mains and ~3starters that are a nice variety to be available on room service. This is especially useful as there are only 3 resturants within walking distance of the hotel (about 0.5miles) - an Indian, Italian and Chinese. There are fast food joints nearby (McDonalds in the same place as the restaurants) and then a few places in the nearby (5 minutes / 0.2 miles) shopping centre including Burger King, a Subway imitation and a large Marks & Spencers with a good food selection (Plus another cheaper supermarket called Morrisons), there is a TESCO next to the restaurants too.

During my time in Edinburgh I have also stopped at the Marriott Dalmahoy occasionally - it is a lovely hotel, much better than the Edinburgh Marriott and very generous with extra welcome presents as a plat (I've had a variety of discount whisky tasting, chocolate covered fruit, welcome beer and a free cheese platter, most of the time at least 2 of these on each arrival), however it is miles from anywhere so unless you are golfing it will probably cost you another £20 each way in taxi fares to the city centre. Public transport is just about an option, but the buses are very infrequent (once an hour I believe, I never tried) and the bus stop is already half a mile from the hotel lobby (as the hotel has extensive grounds and an attractive golf course). I believe they also do free breakfast for plats/golds too just to eat in the hotel restaurant, no vouchers (not certain as my corporate rate may have included breakfast to confuse the issue for me).

I have also spent quite a few nights at the two Hiltons getting my free night certificates. Both are in very good city locations and are much better for a traveller who wants to be in the city centre. The Hilton Caledonian is a very nice hotel and clearly 5*, the Hilton Grosvenor isn't as nice but much cheaper and right next to Haymarket for good train/bus links.