You have a point, for surely poets have sometimes chosen words that don't mean much in order to complete a rhyme. 

The problem is, of course: how does one know when that's the case?

Reductio ad absurdum: Should we discount the meaning of all rhymed words?

Another counter-argument: Rhymes are strategically placed at the end of lines, (usually,) and are mnemonic, memorable and therefore semantically, as a general rule, more important than the other words in the line.