There are problem characters for raw balance and problem characters for feel. Echo is not one of them in the slightest.
Widowmaker/Roadhog/Mercy are problem feel characters. Roadhog had his hook gutted for 1shot ease and many characters have had their one shots tweaked. Sojourn, Widow, Hanzo, Cass, Roadhog, Orisa, Sigma, Reinhardt, and Junkrat.
Pharah/S76 is a problem mid-tier characters. As in, they are rarely an issue at top tier while busted for your middle tier players.
Echo is not busted for any tier nor giving problematic mechanics.