It doesn't defeat the purpose of anything, I rarely partake in the transfer market because every good card I own is untradeable. Most high rated gold rares aren't worth even 40k coins so selling them is pointless when I can use them in an SBC for something I will use. Most packs you get from rewards aren't even tradeable these days, so from my point of view it's better for the game than the current transfer market.
Because of how expensive SBC's are it makes the most sense for me to use my coins for provision packs, that way I can do 81+ double upgrades and the such. They provide me a much better chance to get something usable in an SBC, they are also around so often that they are much more consistent than waiting 3-4 days at a time for rewards to come through and hoping that I get something usable out of the little they give. I play around around div3-div2 in rivals, I get elite 1 or 2 in Squad battles, I get on average 8 wins in champs and often get very little that is useful for all of the time it takes.
I'm not wasting my time doing transfer market business in a game that already takes up so much free time if you want to do everything. I'm not looking around for good buys that will go up in price or anything like that, it's just pointless drivel, and quite frankly it's mind numbing. It wouldn't affect the market as people with coins would still be able to buy and sell as they please, it just offers those without 2 million or so coins sitting around on their account something extra, and I fail to see the issue with that.