Even if keys price dropped to 10pts, adv refines would propably be more competitive option, only because how easily obtainable keys are in grocery shop, wishing tree etc., while refines are limited. You can redeem 1360keys monthly (4weeks x 68k moon coins) just from grocery alone, which covers 1050 monthly key rebate easily. Also when starting from 0 in shop- in this case monthly limit for keys is 30days x 50 = 1500 so you cant even buy out everything grocery has to offer.

Meanwhile adv refines- with sun coins income (4weeks x 5800) you technically are able to buy 154 refines. Shop adds 5 refines daily, so starting again from 0 in shop- you can buy max of 150. Slight difference, here you run out of items to buy, not currency like in moon coins example. Only a minority of players gets good ammount of refines from swb.

That being said theres nothing wrong with doing 1050 key rebates. With refines, on the other hand you usually want to jump from lv7 to lv10 at once to save some resources with wishcredit. That requires 1353 refines at worst. But you only get 150 of them monthly. Thats where the problem lies and why people prefer redeeming refines over keys.