If 1 item is going to cost upwards of 5k to upgrade, the cap needs to be massively increased, like 10k or 20k at minimum. The cap is actively harmful and has no reason or purpose to existing, but certainly if the gear and crests you can acquire within 1 week are enough that you could enter into the week at the 2k cap, and still not have enough to use the crests or items you gained thru that week before running out, it just means the cap needs to be higher. There isnt really a reason for flightstones to exist at all when crests are already sufficient.
They turn what should be positive experiences > new gear, higher item level, yay
into negative ones > Not enough flightstones, cant use the gear i earned, cant get the power increase out of the item i earned, now i have to “re-earn” the power increase AFTER getting the item, making me do twice the work and more chore activities instead of just letting me experience the cool upgrade immediately. This is the same reason reforging was removed, except instead of fixing your stats at an npc in <5 minutes, you now need to do 30+ minute activites to acquire enough flightstones to use your new items