Because the big way to deal with nightmares is: apc, adc, stand with a controlled single/wild player, quickly break the shield and kill him, or let him leave adc, because nightmares themselves are not particularly meat, and if they are loaded with too much meat, their lethality to adc will be less.
Yao is too old to have the ability to make a second assault (for example, building a plane)
Better restraint: raven, werewolf, fire girl, future, cow, electric mouse, nock, etc.
Note: when fighting in teams, you must leave people to protect the back row! Otherwise, nightmares can easily kill adc.