I dont find it ll be a issue since the new combo system will have add up eminity and for sure some skill will be fix as well, not to mention the class are now involve a lot with trail and trail work as a passive skill so that mean trail can give class some special ability as well.

Imo this is the right direction if you think about 1.21 where job as PLD is a tank specialist for example, and PLD will be better than GLA in tanking so I dont really see the issue. All I do hope is SE add something else to GLA so they can be DD in the future as well so they can have 2 role.

also all those thing you said about are theory-craft, and we cant really tell if the system is right or wrong until we use it.

ninja edit: with the 15 skill/class, some skill will be remove, some will be fix and we might get some new too. So keep checking is the best