Simply put, Part OPS will tell you whether you need an EASA licence, Part FCL will tell you how to get one.
Part OPS will
not tell you whether you need an EASA licence. It is quite clearly set out in the cover regulation of Part-FCL, which I will quote one more time:
Article 1
Objective and scope
This Regulation establishes common technical requirements for:
1. the licensing, training and testing of pilots involved in the operation of aircraft referred to in Article 4(1)(b) and (c) of the Basic Regulation;
Article 3
Pilot licensing
Personnel referred to in Article 1 shall be qualified in accordance with the provisions of Annex I to this Regulation, hereon referred to as Part-FCL.