well said
i used to agree that you should have the player do whats more comfortable but since i started going to some coaching clinics at places like Rutgers and Nova and other colleges or places with experienced coaches, i now start really hammering technique starting in the summer and early practice in aug so that it becomes 2nd nature and it no longer feels uncomfortable.
WRs should have their inside foot up, DBs playing tight man coverage should also have their inside foot up. The reason to hammer correct technique is because you want to limit your movements and not waste movement trying to get in correct position. We'll do a lot of quick step back peddling right out of the stance over and over and over just a few steps from stance to stop just so the guys get the feel of how it should be. M drill or W (depending on what your coach called it) is also good for guys getting used to correct foot planting on slant routes. Once you can get the proper technique down, you no longer are thinking about which foot should be forward, it just is habit and you're helping yourself out with your footwork and movement by limiting your steps and putting yourself in proper position.
These college coaches kept stressing technique and reptition and i've noticed a difference in our DBs and WRs being in better position and having better footwork because they are lined up correctly and taking the proper steps, turning their hips correctly, etc.
So while you are right that you want your player to feel comfortable, that could lead to bad habits and improper technique when all it might take is just repetition and practice to get used to doing it the right way so it feels better. As lame as it sounds, you need to practice positioning and stance just like you need to practice the proper way of tackling. Its not something you can just tell someone to do, show them once and then boom they learned it and can apply it. They need to do it over and over and over until it becomes 2nd nature to them. Otherwise they're just practicing wrong technique.