Single seat fighter v Twin Seat Fighter
Western made single seat fighters are the preferred option these days simply because of the high degree of sensor automation and sensor fusion which reduces pilot workload to a manageable level. All of the following fighters, the F-22, F-35, Gripen, Typhoon, and Rafale have very advanced computer systems and cockpit displays which take data from all the onboard and some off-board sensors and present the data in an accurate and easy to read format. Sensors such the AI radar, Infra Red Search and Track, Radar Warning Receiver, Electronic Support Measures and Data Links to mention but a few. Off board sensor information from AWACs would also come via Data Link. These modern fighters take the AWACS data link information and data link information from other fighters using the same system and marry it to all the other information coming into the aircraft to form a complete air picture providing situational awareness for the pilot - all automatically. The cockpit computer display screens make all this possible, the pilot is easily able to select what he wishes to see. So there is no need for a WSO in such aircraft, especially those concerned with Air to Air tasks.
For the more workload heavy tasks such as SEAD (Supression of Enemy Air Defences), Maritime Strike and Interdiction the workload becomes much heavier, particularly as the pilot may be flying close to the ground so that will occupy his attention, the WSO will concentrate on navigation, finding the target through his sensors, arming and dropping weapons, very much a team effort which would be too much for one man.
Another reason why 2 seats may be preferable to one is that some fighters/multi role aircraft these are still very much in the analogue cockpit age which have many individual dials. This alone presents a high workload factor so 2 heads are better than 1 in this respect.
It is true that 2 pairs of eye are better than 1 but with the amount of situational awareness provided by sensor fusion that second person is not needed anymore.