Basically echoing mdcwdzies thoughts and trying to define competitive advantage...
Don't care about cosmetic microtransactions. I never use them (never even dye my armor), and they clearly offer no competitive advantage.
I am fine with things like additional character slots and stash space. This to me is more of a QoL improvement than an advantage.
I think the proposed "timed xp bonus" is just slightly too far into the "competitive advantage" for me, especially in something like Seasons.
Buying gear strictly a "pay to win" and strongly against it.