In that simulated tests there were some very tight restrictions imposed on the "blue force". This test was specially designed to see how the planes would do in heavily outnumbered situations, way out to the limit of their range. The idea was to simulate defending Taiwan from a massive Chinese attack while flying from bases in Okinawa. The test was for close combat at the limits of their range, with very few F22's available, while the red force had "future versions of Suchoi fighters" with better radars then today available.
For the F-35, with the wing loading and power loading close to the F105 "Lead Sled", in a range where the Suchoi radar and missiles could work ok against it's type of stealth, this is a recipe for disaster.
With fewer long range missiles available on the F-35, in an all out war, it is possible for a large enemy force to get in close range.
With better dogfighting planes and more missiles available is not surprising the Su-27 type fighters could be very dangerous at close range.