Yeah, it depends. The vast majority of shooters will be satisfied with an off-the-shelf gun. They will add a few things, but the bones are fine. Of course the AR is the Harley of the gun world. No two are alike and most owners change something. Usually that something does little to the basic operation.
Also, building a rifle is fun, but not for everyone. It requires special tools and some special skills. With the AR those skills are not particularly difficult to acquire. Still, there are tools necessary and the cost of those often out weighs any savings you'll get by building your own.
Further, it's not hard to find the specific configuration you're interested in. Most of the time an AR can be found on the shelf that is close enough to what we really want. Then just swap one thing and you have what you wanted.
Then there are guys like me. I'll never be done building my AR. There will always be another gadget to add or change. Meh, that's part of the reason I have them.