I am sure others have as well, but I have brought this up several times. I like to use Nightingale as an example. My 9* Gale is 200-300 power less than my 8* heroes (all skills maxed). She is 2k~ power less than other 9*. So not only is she a great healer in her own right, she givers your team an overall lower score than other heroes.
If they just increased the power of all the current meta heroes by a few thousand, I agree it would help things. Having a Panzer/Nightingale/Ifrit/Flatline/Matador team that cost 5-8k more points than an equal star/rank team of “lesser” heroes would help balance things out.
Of course I think a number of other heroes still need work. Maven needs a 10-15% hp increase, her silence needs to travel way faster so it can hit more, and her AoE should either slow or stun targets (30% chance to stun for 2 seconds every tick) caught in it.
Clyde needs a 20-30% hp buff and make his skills less all or nothing luck reliant. Make the luck give extra damage, not if a skill will land or not.
Odachi, Hecklar, Sapphyr, and Kunoichi just need 20-30% more hp each. I think changing the armor to a percent reduction, along with an hp increase would dramatically make these heroes viable.