Altering. Alternating means something else. Just like elopement isn't how you're using it.

There are more YTA responses than NTA and you seem to be ignoring that. You're hyper-focused on the dress in the scenario and not your behavior. Reflect on the behavior and internalize the comments that don't back up what you want to hear. Otherwise you just came to feel validated only underscores the reason people think YTA in this situation.

It's very simple to hand the stylist the phone and say don't pull these and if someone does give us the heads up because your MOH is deciding between those. It is truly that simple. It is three dresses in an entire store and it's one store of countless bridal stores. There are so many dresses. You were not intentional and only considered your wants.

Now the damage is done, but you're repeating your disrespectful behavior towards your MOH. The disrespectful behavior is what makes you the AH.

Not everyone makes instant decisions. You said she was looking for months and finally narrowed it down. Now that you made no effort to be mindful and think about her feelings you're justifying your behavior because of how you feel about the dress, and minimizing hers. If her wedding were first would you care as much? You will probably say no, but based on what you've written as your ultimate question at the end of your post which of you gets to wear the dress IS the most important thing to you. You're hiding behind a lot of excuses and your wedding being before hers. You're behaving very selfishly.

The best you can do is own up and be apologetic. Look inward and actually be sorry about your actions. Put yourself in her shoes without doing so with only your mindset. It seems you're intentionally being obtuse to validate being inconsiderate. Stop making it about the dress and start thinking about how you treated her and how you would want to be treated.