It is true that no one can be completely certain of the original pronunciation.. However there are some important differences between the 2 names.
The largest difference in my view is the "hey" Or the H in YHWH. Hebrew words and Letters all have intrinsic meanings and symbolism's, some of the meanings and representations of "Hey" are..
"Hey represents the divine breath, revelation, and light (the word "light" is mentioned five times on the first day of creation (Gen. 1:3-4)"
Hey represents Gods creative power .. " In the Talmud (Menachot 29b) it is said that the "breath of His mouth" refers to the sound of the letter Hey - the outbreathing of Spirit."
"Hey functions as the definite article in Hebrew, a sort of demonstrative that points to the object and makes it concrete and definite."
The ancient Semitic pictographic version of "Hey" looked like a Man with his arms reaching to Heaven, or in a stance of praise and thanks..
By removing the Hey and the 2 other letters You take away any Living characteristics or symbols from the name.