The new gear bonus is fine! It's a nice touch to add a little damage to the new weapons, or a bit damage resist to the new armour. The old gear will be just as useful if the bonuses existed or not... having the bonuses is quite literally a bonus! Consider it a free artifact perk for extra weapon damage, for example. You might be insinuating the next bit, and apologies if that's the case... but it feels like the negative aspect comes from the tier system. So if you want tier 5 gear with seasonal bonuses and set bonuses (on the armour), then that's a pretty repetitive grind season by season (or dlc by dlc).