But one can over shorten the readback, which may indicate a misunderstanding of the information given by ATC, thereby further cluttering the airwaves while confirmation takes place.
AIP GEN 3.4 - 4.4 Readback Requirements
4.4.1 Pilots must transmit a correct read-back of ATC clearances, instructions and information which are transmitted by voice. For other than Item a., only key elements of the following clearances, instructions, or information must be read back ensuring sufficient detail in included to indicate compliance.
a. an ATC route clearance in its entirety, and any amendments;
b. en route holding instructions;
c. any holding point specificed in a taxi clearance
d. any clearances or instructions to hold short of, enter, land on, conditional line-up on, take-off from, cross, taxi or backtrack on, any runway;
e. any approach clearance;
f. assigned runway, altimeter settings directed to specific aircraft, radio and radio navigation frequency instructions;
Note: An "expectation" of the runway to be used is not to be read back.
g. SSR codes, data link logon codes;
h. level instructions, direction of turn, heading and speed instructions.
While I certainly agree that too much is read-back "word-for-word", in CC's shortened readback example, I'd argue that sufficient detail is not included to indicate understanding and compliance with all parts of the instruction (e.g freq change when leaving).