why karma's shield AP ratio is lower than other supports?

gutted.

but still brok

sona's entire w.

They buffed it up in the new patch that is coming. I think to 0.9

You make it sound like she only has 1 shield... There's also the 0.8 mantra shield.

Not sure where you're getting this 0.6 ratio from either. Thresh is 0.4, Sona is 0.2, Orianna is 0.4, Lux is 0.35, Lulu's is 0.6, Morganna is 0.7, Janna is 0.7. Only a single 0.6 in the bunch, and her ult is essentially an HP shield with a 0.5 ratio. Also nobody in that group has a shield with a ratio as high as 0.8, which is Karma's Mantra shield. That also applies a 0.4 ratio shield to the rest of Karma's team, more reliably and with a higher ratio than Lux's AoE shield.

So:

why karma's shield AP ratio is lower than other supports?

Karma's shield AP ratio is not lower than other supports. Her basic shield is pretty average compared to other supports, and her empowered shield is arguably the best HP shield in the game.

Misleading question is misleading.

E ap ratio is 0.5 E with mantra ap ratio is 0.8 (which is the best ap ratio on a shielding spell)

Cause they didnt want her to have a strict identity, they are ok with her being a support but wont give her any of the perks, she doesnt get improved mana regen like other supports,she doesn't get ap utility scaling like other supports,and she doesnt get a good shield like other supports that have higher ratios and their shields last longer

My guess is the movement speed it gives compensates for the lower ratio.

move speed and somewhat spammy.

because of the cooldown