I don't say don't do sport, I say do trad before sport if you want to be a trad climber.
first reason: In trad falling can be dangerous specially if the first pro pull out. Knowing how to fall on your feet will minimize the kind of injury that you will have. Falling in your back and you can be paralyze for the rest of your life. So, climbing on your feet and knowing how to place your body to jump or sleep safely is very important. Of course, you will feel more confident if you climb 5.9 before you do your first 5.6 lead in trad and, fortunately, the risk of falling is very low on that kind of route. But it is when you have to decide to do a move where there is a danger that you will learn all the process of being safe. After that, you will understand the progression: using your hips to protect vital part of the body, looking for a move using three point of contact before two points, understanding the difference between intermediate and advance move, using your power when one hold is missing, using your body in equilibrium as a single point of contact. I most say that sport climber learn by imitation of other and will learn technique adapt to a bolt protection situation. In general, sport climber don't make the distinction of being in control of his safety and using a bad technique for the problem. They will need bolt
second reason: a little bit technical, When you climb, you need energy. It is like someone who run. If you jog, you will use aerobic energy and will be able to perform for hours. If you played soccer, you will run faster and stop and go. There is a chance that you will be out of breath. Finally, in a 100 meter race, you will use a very fast kind of energy. Those energy are call aerobic, anaerobic lactique and creatine phosphatase. When you climb on sport, you will use the second and third one mostly. In a trad route of 8 pitches, you will use more aerobic energy and in some places creatine to climb a short hard section and anaerobic to look where you are going for the next hold. any other way to explain it?