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If you check out the $\mathrm{p}K_\mathrm{a}$ values of paracetamol (acetaminophen) , it is 9.38 while $\mathrm pK_\mathrm a$ of para-methoxybenzene is 10.1.

So, $\ce{-OR}$ should exert a greater mesomeric effect as compared to $\ce{-NHCOR}$ making the wikipedia wrong.

References:

1. https://pubchem.ncbi.nlm.nih.gov/compound/Acetaminophen

2. https://pubchem.ncbi.nlm.nih.gov/compound/4-Methoxyphenol#section=Ionicity