If you fill a fabric pot to capacity, you don't have problems like soil loosening up. By the time you need stakes, the plant will have rooted the pot and will hold the soil in place.
You need to have them in some sort of pan or tray or whatever when you water, because to thoroughly wet the soil, they might have to sit in some water to absorb it all (and they do tend to absorb it all) and moisten the entire amount of soil. When watering from the top when the soil is dry, it will run down the side of the soil mass and pop out various places through the fabric. This does NOT mean you have thoroughly watered it. The water just found an easy route.
I've used both fabric pots and hard-sided. I can't say I've seen any noticeable increase in yield from fabric, except that they tend to hold more soil than advertised. I have some 5 gallon pots that really hold 7, for example. More soil = potential for higher yield.