...and not being a healing/shielding bot, then don't buff Janna's damage, just to nerf it and the shield later. It is not very hard to choose which skills to max first when the shield is on 18 seconds cooldown lvl 1 and gets 2 second less per level. The exact same thing happened to Soraka. There is litterally no reason to max Q on Soraka or W on Janna now, which means that you are not doing enough damage to worth the risk of getting caught out when poking. Now you are also nerfing Sona's damage, one of the squishy support who's playstyle is not about standing behind the adc.
Me, being a god of staying behind adc(I actually like that playstyle, don't judge), got forced to play offensively when janna's damage got buffed, which was a great experience and not too bad, but then got forced back into standing behind adc when her damage got nerfed right after. What is the difference between now and before? Nothing, expect that the heal and shield got a longer cooldown, which is just a direct nerf with pretty much no compensation.