Air seeping around the door is a non-issue. Vents should still need to be opened, if only a little. Air blowing in is another matter. A simple wind screen fixes that. If air is not blowing in and vents still need to be closed all the way the cooker is either in hot sun, too much lit fuel was used, there's an out-of-round issue, or a combo of two or more of these.
WSMs are easy to cook in. Like kettles, offsets and other coal- or wood-fired cookers one needs to learn to cook within a temp range, adjust for ambient conditions, structure the start-up of the fuel effectively, etc. Imo, those things - along with the flavors produced - are what make cooking outside so enjoyable. Cooking on coal- or wood-fired cookers requires a fairly easy-to-lean skill set. It's just practice and understanding. With it one can cook on anyone's cooker of any type anywhere.
Making the WSM a perfect little dial-it-in oven is certainly possible. I wouldn't fault anyone for taking that approach. But it is far from required or necessary.
