You people are like game show winners, except now you're belittling the people who work hard at their jobs to buy the same thing.
"Omg! I totally EARNED my car! I had to like, stand in line for the game show for hours EVERY day! And I didn't even win anything for weeks! Gosh, all those people who pay for their cars with the money they earn from their jobs have it totally easy! All they have to do is like, get the money and then buy it whenever the car goes on sale! Unlike us, who had no idea when we would win our car, and had to spend months attending game shows with no guarantee that we would get anything. That's SO much harder than getting the money to buy it."
You're basically "earning" lottery tickets. You may have earned the right to win by purchasing the ticket, but you didn't earn the money itself.
In other words, you didn't earn that Exotic weapon by playing the game. By playing the game, you earned the chance to [i]win[/i] that item. Just like by earning strange coins, you have earned the chance to acquire whatever item Xur sells.
TL;DR
You don't [i]EARN[/i] Exotic weapons by doing in-game activities, you earn the chance to [i]WIN[/i] Exotic weapons by doing in-game activities.
There's [i]ABSOLUTELY NO DIFFERENCE[/i] between the two methods.
/rant
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I agree that there is no difference between the methods in terms of having control over getting what you want. The difference is that getting something via RNG is much more difficult than getting 23 strange coins. If you are simply looking at "expected time to obtain" as a metric for earning, getting something via RNG wins hands down.