That's simply following standard practice — it doesn't mean I cut corners.
Literal
That [topic-は] standard-play according-to [quotative-という] just [with-で], hand [object-を] pulled-out reason is-not.
定石 (joseki) originally refers to established sequences in Go, but is widely used for 'the standard approach.' 手を抜く (pull out one's hand) means 'to cut corners' or 'slack off.' ~わけではない denies an inference: 'it doesn't mean that.' The ~というだけで frames the first clause as a mere description, not an admission.