Can we see the game getting additional complexity on the strategy of battle classes like skillchains or elemental affinity of monsters?

Very few games with the exception of FFXI and D&D offer complex battle strategies between players and enemies. I know your goal is to ensure every job is valuable in a fight. You can easily do this by ensuring all jobs have access to 4 of 8 elements by LV20.

Example: Ensure every mob has two elemental weaknesses (if any) so every job can have at least 1 of the matching elemental attacks (or spells).

Crab (Aquans) -
25% Bonus DMG to Ice Attack (best)
15% Bonus DMG to Thunder Attack (good)
15% DMG Reduction to Earth Attack (bad)

Skillchain:
To make a fair playing field, increase dmg by a nominal 5% per Chain until the chain is broken or perhaps doesn't match.

This type of play style doesn't exist in any game but a final fantasy game. This should exist in FFXIV!