People who dress up have a huge advantage over who dress casually, not that it is bad that you wear casual clothes, it’s just that looking good can do wonders for a person. Look at it this way, if you were going to a job interview, and you were with another fellow applying for the same position, and let’s say you were wearing something casual and the other person wore something sharp, if you have almost identical qualifications, the one likely to get the job would probably be the other person. An air of confidence created by the clothes he wears would be his only advantage for you, with this you will learn that next time it would be much better if you wore one of your custom shirts to make you look better. Try it and see the results of this yourself.
Having a huge wardrobe is usual for women. For men just a number of custom dress shirts would actually do the job. He would just need to be creative in combining his shirts with pants and shoes to make it look like that he has a lot of clothes to wear so that he can look a lot sharper.