6 awg NM-B (aka Romex) is rated for a max circuit
size of 55A and cannot be used with a 60A breaker.
Specs from the Southwire site:
View attachment 1056
The factory cord is designed for a max circuit of 50A.
Running without a plug/receptacle IS safer, but requires the proper wire and installation method. Hardwiring is the only approved method of using any EVSE at 48A (or above).
There are two main problems with this install:
1) Wire is undersized for the load
2) The wire type/rating is not allowed for permanent wiring, in wall use, and a variety of other issues (See NEC 400.5, 400.7, 400.8 as a start)
Unless permitted in 400.7, as described in the previous paragraph, 400.8 states flexible cords and cables shall not be used as a substitute for a structure’s fixed wiring; run through holes in walls, structural ceilings, suspended ceilings, dropped ceilings or floors; run through doorways, windows or similar openings; attached to building surfaces (except in accordance with 368.56(B) from busway plugs to equipment with extra-hard usage cord or listed bus-drop cable); concealed by walls, floors or ceilings or located above suspended or dropped ceilings; installed in raceways except where specifically permitted elsewhere in the NEC; or where subject to physical damage.
The purpose of most requirements in 400.8 is to ensure the flexible cords or cables are readily visible for inspection for damage and other problems with the cords or cables. Concealment of flexible cords and cables has been an NEC violation almost from the inception of flexible cords and cables.
As I stated before, it is unlikely that a fire will result from this install.
BUT, the likelihood of a fire is magnitudes
greater than if a proper installation was done.
The fact that someone would do this at all would lead me to question other details of the install like proper strain relief, torque on the connections to the breaker, etc.
6/3 MC cable is less $5/ft. The OP saved <$20 by having a "creative" (aka half a**ed) install done.