With Sektor, 3 hit pop up,deep JK, HK = free smart missile and it does more damage than Cyrax's chain. Sektor owns Cyrax with missile lock down, as Cyrax has no conventional way to prevent homing missile spam, and obviously P1 Sektor can abuse homing + smart missile combination. Sektor does not have to leave the ground or use teleport punches to beat Cyrax, but teleport punch is available on bombs and nets. Cyrax's strengths, trading hits for the net, the bomb break infinite, throw tricks like you mentioned, other than that not much except using bombs similary to Sektor's missiles. Neither of them should really ever leave the ground vs eachother except to avoid eachother's zonine, in which case Sektor's potential is greater midscreen. The distance from which Sektor should fire a homing missile when Cyrax is neutral does not allow for a counter with a net, and even still, the uncertainty in the chance that Cyrax's combo will beat the missile's collision is there.
As for Mileena vs Sheeva:
Mileena's roll is > all Sheeva's specials.
Mileena's Sai Shot lock down is generally effective against Sheeva, as Sheeva cannot run in while Mileena is doing them even erroneously high.
Mileena can upward JPS to combo Sheeva.
Mileena can roll under Sheeva's fireball.
Mileena can bait aaHKs with the Sai Shot.
Mileena has a longer sweep range, plus her sweeps are silent.
Mileena has a longer standing HK range.
Mileena has a longer standing LK range.
Mileena has a longer uppercut range.
Mileena has superior run jabs.
Sheeva is highly vulnerable to female ninja corner run jab lockdown.
Sheeva's knee lift whiffs when Mileena is getting up if she doesn't block or duck after a sweep.
Sheeva cannot cross up Mileena because of the roll.
Sheeva cannot do grounded JK to full damage teleport stomp vs Mileena.
Sheeva cannot do throw to full damage teleport stomp vs Mileena.
The Ground Stomp has a 1 frame or so chance of catching Mileena when landing during Sai Shot spamming.
Sheeva's HK misses Mileena on a ducking block.
Sheeva's standing LK, HK and sweep when blocked are punishable by the roll.
Sheeva has higher damage ground combos.
Two of Mileena's moves are punishable by juggle.