I bolded the part I don't agree with.
Indeed I believe that such bolded part a key element in the sentence.
IMO, expression is not an accessory to music, but is its core function. It's not something that gets added on at a later time, but rather is something that needs to exist in all forms of musical delivery, in all stages of learning and development. It is what differentiates a collective of pitches, rhythmical patterns, and mathematical relationships, and transforms them into a communicative medium.
Metronomic pulse is indeed essential to our understanding of musical organization, but it is not point of music.
I think one of the key elements in musical expression is awareness. Especially in the art music tradition, we are often urged to chase after idealistic interpretations - that these "masterpieces" we play require such respect. Ironically, it is quite often that this obsessive desire is what ends up choking the music we so much wish to emote. Musical expression is not solely about planning and executing the perfect game plan, but it requires us to be aware of the very thing we are doing. Music is influenced by so many elements out of our control: the acoustic space, our instrument, the prevailing environmental conditions - that need to be included as part of the music making process. Stubbornly dictating our idealistic and perfectionistic desires with reckless disregard towards awareness in-the-moment does not do anything good for our music.
So how does this relate to the metronome? It is a tool used to help us understand music better, however it is not the goal nor the prerequisite to music making. Expression is not something that emerges out of metronomic exactitude, but rather is the heartbeat of music itself.