Fear of interception !! Aren’t russian su-27 and Su 35 supposed to be doing 24/7 patroling in Ukrainian airspace. This reminds me of Indian AF doing operations inside Pak airspace without proper firepower and half-hearted effort at best. I feel that Russian AF will be miserable against a proper western airforce.
Well it can be that SAMs are still operational in Ukraine. Transports will definitely be a major target. This begs the question of why are these sites still kicking and not destroyed by SEAD sorties. Or why Russian ECM planes are not doing their job.
The Ukrainian AF is still in the fight (or was still in the fight a few hours ago). Whether they pose any threat to VVS in the air is questionable. As you said, Su-35s easily outclass the Ukrainian Mig-29s.
As for the last point, there is a reason why the PLAAF has adopted to NATO training styles.