Until we have more information about how the Ventures work it is difficult to determine whether this could be P2W or not. If for example the gear the retainers wear increases in spirit bonding this would be a big problem, and allowing extra income in gil absolutely provides an endgame advantage early on. Many players which ignore gil as a factor may see this as having no advantage, but until you have full gear from T6-9 or new tomes (both being limited) it will matter.

Assuming ilvl90 crafted gear can be penta-melded (think level V materia), if I have fully melded ilvl90 gear I will (initially) have a CLEAR gear advantage in endgame content over your full myth/allagan gear. All my tank gear could have max parry and accuracy capped, better than current BiS etc. Any boost in gil by paying real life dollars is paying to win, in this case, since materia prices will (probably) be very high. Once more info is revealed, it will become more clear whether there will be much of an advantage at all, but discounting the fact that this could in no way be pay (with rl dollars) to win (have an advantage over others with all else being equal) is just ignorant bliss. More facts are needed to make a true judgment of course, but this is just an example.