Custom made suit question

I was recently fitted for a suit by a tailor that a user recommended. I tried the suit on for the first time today and was pleasantly surprised. The construction quality and fit seemed really good. The only "problem" was that the jacket was a bit boxy on the sides, whereas I had asked for something a little more tapered. This particular tailor did not do a mock-up in cheaper fabric before cutting the fabric, a process that would likely have avoided this problem. When I brought the problem to the tailor's attention, he just pinned it and said he would make the alteration and that I could pick the suit up the following Monday. My question is this: does it defeat the purpose to have a custom made suit if the tailor is just going to alter it once the jacket is finished? Is the akin to buying a jacket OTR and having it taken in to make it more tapered/less boxy? Or, since this is my first time having a custom suit made, maybe it is not a big deal and totally to be expected. Thanks for reading.