I have heard this logic before, defending over-engineering the looks to hide a brittle backed. Both sides look very entrenched on their position, I lean more towards having a solid backend and see the polished frontend as a waste of effort, but I understand your logic of seeing it as professionalism. My point is that you are not sending only one message by using a cheap slop static html: some will see lazy and cheap people, some will see people focusing on the real thing with no time or willingness to make shiny sites.