Your simply creating a myriad of conditions that the adc has to compete under.
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He has to avoid damage while farming.
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He has to time his last hit to secure gold.
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He has to watch the map for M.I.A and be wary of a potential ganks.
And as if all that isn't enough to worry about now hes supposed to compete with the very person that is supposed to harass the enemy bot lane and protect him from damage so that he can farm.
Yes there are situations in which the person clearly has no idea what they are doing.
Currently trending is a parade of supports that will blast every CD and Sum Spell to ks their adc, for instance the raka's in my games lately can heal the adc and still "secure the kill". They like to sit there and bust their Q/E while their adc is nuked, never send out a single heal, ks watch adc die then bust their ult so they themselves can get away.
There is absolutely no reason for this type of behavior, if you don't want to play support then no one is making you. You will get one of two chosen roles. Don't pick fill and move on.