Do you think after Endwalker there will be time travel?

[Enkidoh]

Most of our combat knowledge comes from the soul Crystal, we haven’t actually mastered these styles we’re just borrowing the memories of the people who have. The only skills that are our own are the class skills and anything from machinist since we are the one putting our memories into that soul Crystal.

Yes and no. The Soul Crystal does act as a skill repository from past practioners of that Discipline that a user can draw skills quickly from, but you're also creating skills yourself as you go along, which are then recorded in the Soul Crystal, via a process similar to attuning to an aetheryte. And MCH and BLU's Soul Crystals you are literally creating everything from scratch then and there, given both Jobs have been made virtually from out of whole cloth unlike other Jobs that are just Disciplines that had been lost, forgotten, were foreign and unknown in Eorzea or made illegal.

MCH is the WoL testing Stephanivien's new theories of aetheromachinestry derived from Garlean magitek that he melded with a few Limsan musketry techniques (from the strictly controlled/forbidden Discipline of Musketeer), while BLU was actually a fake Job (but based on a real one from the New World) peddled by a con artist that we actually made completely functional, much to his relief, given the Limsan authorities were circling.

So the WoL is not just 'drawing on older techniques', they're actually adding new ones they make up themselves, and other NPC practioners of the Jobs are shown doing the same thing, making use of skills and spells we have no access to (and never will). Most of our combat knowledge and skill just comes from plain old determination and a bountiful reserve of personal aether, something the Soul Crystals only enhance and amplify (that the Echo and the Blessing of Light enhance even further).