There are multiple reasons not to ditch conventional fighters altogether even with stealths.
Just a few of the obvious ones off the top of my head:
-Stealth fighters can only carry a limited munitions load in terms of both quantity and size internally. If you start hanging weapons externally, you might as well be using conventional planes.
With a mixed fleet, the stealths can range ahead and act as spotters to cue up conventional fighters acting as missile carriers to shoot super long range AAMs at enemy stealths from beyond their internally carried missile ranges.
-similarly, conventional planes can carry dedicated jamming pods to enhance the survivability of both your stealth and conventional jets.
-modern radars have LPI scanning modes, but in order to remain LPI, there will be some sacrifices in performance compared to zero restriction, max performance mode.
With a mixed fleet, you can have conventional fighters like the J16 use their radars at max power and datalink the results to nearby J20s.
Any enemy stealth that wants to take a crack at the J16s will announce themselves to the J20s.
-with the limited munitions load and numbers of stealths, combat persistence becomes an issue.
With a large fleet of conventional fighters, you can tag team the enemy.
Planes like the J10 could be held back in reserve, initially to protect high value assets like AWACS and tankers, but after the main fighter groups have engaged, they can boost forward to join in the fray when both sets of stealths are locked in WVR dogfighting.
With enemy stealths already locked in WVR, they can close with minimal or no interference, and could even only carry WVR loads.
Their arrival would allow your stealths to disengage to rearm and refuel, while the enemy stealths are forced to fight on with guns only or risk turning tail and presenting easy tail shots.
