There is many instant kill Mechanic in this game, so even with Echo buff it doesn't help if you don't know the mechanic and everyone know the fight. Having more Echo buff sometime even make the fight even harder since most boss they shift phrase with certain HP Percentage. Take for example Twintania, Levi Ex, Titan Ex, etc.

The Echo Buff just help eased the DPS check and less healing. If you can't dodge and know the Mechanic, you will still wipe regardless. There are people who still stuck on T5 and Titan Ex. This is why the Echo Buff does not help. It also the reason they remove the requirement to advance in 2.3.

So no, the Echo Buff does not hand you the victory. It just eased up the fight a bit.