You shouldn’t accept ridicule from cyclist who think they know just how important the seat tube is on a bike. For example, did you know that currently the humble seat tube is one of the most design focused areas on a carbon bike (I refer to established brands). Granted the new Cervelo P5x TT bike has done away with it but if you are a UCI compliant cyclist the seat tube is here to stay. Why so important? The biggest gains on UCI compliant road bikes these days comes from a more comfortable bike. Advances in aero tubes, BB stiffness and weight are well developed compared to rider fatigue. This is the no 1 enemy of competitive cycling. Trek’s development of the ISO Speed system in the Domane and Madone 9 is an obvious example of minimising rider fatigue without compromising frame stiffness. The genius of the Madone 9 with it’s internal flexi tube and external aero cover allows relative comfort on a sprinters bike. Another myth is that thin seat stays provide a softer ride. The purpose of the seat stay is to push back (stay) the over-flexing seat tube. It does not allow the chain stays to flex as some think. The new thinking is to design the frame around the seat tube!
The more relative point from a carbon repair perspective is if you find a fracture anywhere on your seat tube, you should seek advice immediately. The seat tube flexes like a bow when stressed. Any flaws or cracks in the tube could compromise the structure of the whole frame. A bit like a house of cards.