Re: Is loss of meter in poetry "decay"?
As a preliminary, it might be necessary to establish the meaning of "metre", in the proposed discussion.
For example, English verse between 1500 and 1900 is predominantly accentual, i.e. its various metres imply certain patterns of stressed and unstressed syllables.
On the other hand, Virgil and Euripides might well have found accentual verse slightly crude, as they were accustomed to verse measured by quantity, i.e. by the length of syllables. (Then too, while English verse has made much use of rhyme, rhyme was generally avoided in Greek and Latin poetry.)
Again, in the prosody of the Romance languages, e.g. the French alexandrine, metre is defined in terms of the number of syllables, and its effects are likely to be lost on an audience accustomed to English accentual iambics.
Not a professional ESL teacher.