You can conclude There exists no PTAS for Problem P1 if $P \neq NP$, but you can NOT conclude P1 is APX-hard. Precisely: If someone proofs $P = NP$ you get a trivial PTAS; Assumung $P \neq NP$, it still could be APX-intermediate (see https://en.wikipedia.org/wiki/APX#APX-intermediate).

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