That's fine providing you live in a country that has (or skydive only in) fine, warm weather. Try this in UK during most of the year and you will probably be glad for an extra layer of protection from the elements!
Also, I presume you are not flying naked? And so any clothing you wear will act as friction to the passing air - so a jumpsuit merely provides a consistent friction across your body surface.
If learning a new discipline then surely consistency across as many variables as possible is a desirable as this allows the student to adopt the basic principles. Wearing different clothes will affect these variables and make it increasingly difficult to get to grips with the basics and that's when bad habits are created to compensate for the lack of basic knowledge.
Bad habits are generally adopted due to non-existent or bad coaching and not because of the threads you wear (I am sure there are exceptions to this but I am generalising here).
I will finish by saying that not wearing a suit is great and fun and far less restricting in movement but, learning the basics and progression must be learned from a stable platform and non-suit flying should be attempted only after the basics have been mastered.