I don't agree. The pause between lines often enhances variations transpiring in the poem. Because I find the 6-line style visually appealing, many of my early sijo were presented this way. More recently, I find myself favoring the 3-line format. Clearly though, the 6-line format is a Western development.
End rhyme is an experimental technique aimed at pleasing Western readers.
However, as this tends to pour the Sijo into the same mold as North American and European poetry, I feel end rhymes infringe on the uniqueness of the form. That is not to say I'm against end rhyme in sijo. On occasion I use it in my own work, finding that a poem sometimes demands end rhyme. But two rhyming lines per poem seem quite enough. To my ear, more than that becomes tiresome.