The issue you have if you're a smaller brand only offering one or two bags, is that you need to try cater for everyone. Not having wheels may lose you sales, but having them doesn't mean it can't be used as a duffle. Personally, it really annoys me when people take kit out of std duffles and the bag just spreads all over the floor (especially in tight changing rooms). So i prefer free standing ones to save space and also protect kit a little.
My first bags were pretty big (like 95x40x40), but there was feedback on here that someone still couldn't fit all their kit in. So maybe better to have more room than not? Appreciate some people will want smaller bags and they are out there. However, i feel people are taking more kit than ever these days and so bigger bags are generally required by most.