Since full potential Anakin is a myth and nothing more we don't know, but I suppose Nihilus could drain him, at least with Luke by his side defending him.
Ok I'll try a similar one.
Obi-Wan at the age of 80 (let's say the Empire never came to be and Obi trained as much as he could) versus Dooku (he's as old as he is in ROTS).
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Yes i think Anakin at full potential would be very close to Luke, Maybe Anakin would be even stronger but this is just speculation. Since you forgot to post another versus, i guess i will do a similar one: Anakin Skywalker(full potential + full training) + Luke Skywalker(NJO) + Leia Solo(Fully trained at full potential) vs Marka Ragnos (at his prime) lol the ultimate skywalker family at their full potential vs the greatest ancient sith lord at his prime.