Like any language, byzantine chant has its own grammar. Oal dhu anjhels in heven danseng and vaere glad tudae.
Reading byzantine music in western notation is like reading a direct translation from another language with poor spelling and grammar (like the phrase above). The reader reads the direct translation silently and then uses their knowledge of English grammar to say the phrase correctly. The brain has to take an extra step to decipher the poor spelling in addition to fixing the grammar.
At the very least, chanting from western notation provides the chanter with some written framework to work from. But, just like in the example above, the brain has to use more processing power when one chants from western notation. In staff notation it is generally assumed that tones are half or whole steps apart and and most music is written using a major or minor scale. This is the "grammar" framework of western notation.
Byzantine chant uses many different sounding scales with tones that don't fit into the half/whole step paradigm. Byzantine chant is built on a tetrachord system instead of an octave system. When byzantine chant is transposed onto a western staff readers have to try to forgot the corresponding western music theory and super impose byzantine chant theory.
Like any language, byzantine chant has its own alphabet, and orthography. Oal dhu anjhels in heven dans and ahr xseedengle glad tudae.
In this example the grammar has been fixed but it is still not easy to read due to the lack of standard spelling.
Reading byzantine music in western notation leaves readers without the orthography rules that enable reading fluency. Each symbol in byzantine notation is like a letter of a written language. Like any spoken language, there are rules for how these letters can be written. This allows one to read chunks of notes together like words--making it easier to sightread unfamiliar music and texts at a rapid pace. The standardized spelling rules also allow sight readers to predict what they will see next. When byzantine chant is transposed into Western notation most of the benefits gained from the orthography of byzantine notation are lost. In addition, reading byzantine music in western notation is like reading Arabic phonetically written out with English letters. Some Arabic letters have no equivalent in English and have to be approximated.
Like any language, byzantine chant has its own cultural background and ethos. All the angels in heaven dance and are exceedingly glad today.
In the Western musical tradition, dynamics are very important to the ethos of the music. Thus, there are many symbols used to notate differences in dynamics. There are no dynamics in byzantine music. The ethos of byzantine chant is found in the flutters and undulations of the voice. These flutters have their own symbols and are easy to sightread in byzantine notation. Often when byzantine chant is transcribed in western notation these flutters are completely omitted. When they are not omitted they are not as easy to read. Reading byzantine music in western notation is like reading the abridged edition of a classic novel. The language and or plot are often simplified to make it easier to read and the depth and fullness of meaning is lost.