I-beam wings have the advantage of fairly quick, easy construction- just one rib template, generally no cap stripping, solid trailing edge. Downsides are the whole plan must be jigged on a flat surface at once. Many, many glue joints. Not very sturdy to mishandling such as trying to pick up by the wing with one hand, tend to be more warp prone and require a tautening covering for strength- not good candidates for plastic film covering, more prone to real "bag of balsa chips" in a crash, easier to rebuild if the fuselage and tail are mainly intact.
Berkeley even kitted a couple of I-beam combat planes back in the 50's. Not really suitable for that event but would make good sport planes. The Lancer was profile I believe.