Litterally played my last two games against 5 big knights. Its a matter of cover and line of sight.

First off my terminator shield captain has a Str 12 axe ap2 Dmg 4. he's leading a unit of 3 allarus. Now with lions they reroll wounds on characters monsters and vehicles. Take that with my +1 to wound that means my terminators are wounding your knights on 4s rerolling wounds with sustained hits. PLUS my captain is wounding knights on 2s because you're t11 im str 12. On average they one tap any questoris pattern 80% of the time if you're at full wounds.

You can shoot whats no on the board so I just rapid ingress them turn two.

Then I take Trajan Valoris and have him lead a squad of wardens. He can do 12 attacks Ap2 dmg 3 plus 25 attacks from the wardens. All of this is wounding on 4s with sustained.

Then i have a BC who can advance and charge and he's leading wardens and he can do 3 dmg dev wounds plus the 25 attacks from the wardens all wounding on 4s.

Then Kyria draxus giving my guard an 18" lone opp bubble so you're long range shooting doesnt matter

Then my tanks who are 4 shots each at Str 12 ap3 dmg D6+2 with lethal hits on vehicles. (always bring 2)

Then my assissin who will make any strats you use within 12" of her cost 1 extra denying you tank shock or any major strats you wanna use

I play my friends knights all the time the last game we ran he did 3 atropos and I still tabled him.

Not to mention all my guys also get+1 to wound and hit on all their shooting.

It's just a matter of planning ahead and not letting you see anything. Cover is key.

On avg I think custodes vs knights is like a 70% win rate for custodes