Right now SI is somewhat limit with respect to other traffic. I believe the devs are/will be working on handling traffic for the future but I no do believe it is a simple task.
I guess it really depends on where you like to fly. For me I tend to fly GA’s and helicopters and generally do not fly into and out of major hubs with high levels of traffic. For me the added immersion of SI works really well and while it would be great if it did interact/control AI traffic it is not a major problem to me. That said I can see the flip side for those you like to fly tube liners in and around traffic. VATSIM is probably the better option for this.