Logan was a great character and contributed wonderfully to my favourite season. But of course none of them compared to Palmer, who we all want our leaders to be like. The writers didn't want just want the same President portrayed by another person though.
Don't forget it wasn't Palmers death that led to a change of President, he'd already resigned and come back at the back end of season 4 to help Logan. There wasn't really anything more that could be done with his character.
Hayter did however say he was disappointed they killed his character off.
God what was I thinking!? Logan was amazing. One of the great acting performances. I guess I was referring to Season 6 onwards.