I agree with this. It's already in canon in TOS that a constitution class could destroy a planet it stands to reason later Starfleet designs are just as capable. Using shipboard phasers and torpedos instead of a relativistic mass allows the crew to fine tune the amount of damage they want to inflict from glassing a whole continent down to surgically stunning a gang of Chicago mobsters.
Kinetic impulse weapons
"Full Impulse" is generally considered to be 0.25c....