I think you are missing many of the benefits of being a repeat customer.
In many cases, I'll take a United flight if there is up to a $50 or maybe even more difference. Between having a United credit card and flying them relatively often, I get a bunch of things that I don't get on any other airline (except southwest). Free checked bags have actual value. I may not use them every time, but even on shorter trips, I often like to buy local beers that aren't available in my town which can't be carried on (and if I am not going to check bags, I can go with the cheaper flight). I get priority boarding and extra privileges when it comes to changing seats/flights. Priority boarding is super handy because I seem to end up on a lot of planes like CRJ-700s where you will get stuck gate-checking your carryon if you are in a late boarding group. I get a couple lounge-passes a year...not helpful most of the time, but great if a flight gets delayed or cancelled (both for somewhere to hang out, and because the customer service agents in the lounge are more helpful than the ones at the gate). $200 difference on a $300 flight? No way, save me the money
And in terms of employer paid airfare? Who cares. When I have travelled for work, I generally fly whatever airline has the times I need...it isn't about the price, it is about the flight that gets me there in time for the meeting...never heard a client complain that I could have saved $200 if I took the 5AM flight instead of the 7AM. If there are multiple options, sure, maybe I would opt for a slightly more expensive United flight if I wanted the extra benefits....but that cost difference pales in comparison to the cost of me going there (since my time is billed hourly). Finally, if you have status, you could actually be saving the company/client money. For instance, say that my boss only flies business class. If he has enough status on one airline to book seats that get upgraded...he can book a coach fare and get upgraded for less money than the business class ticket.