You are very much correct. Do not under any circumstances close the dispute until the item is received the way it was described. If the seller insists on threatening you with not receiving unless you close the dispute, report them to ebay. I hate sellers like that, they make it hard for ones like me. If the seller states his handling time is one business day, that is what it should be. When 2 days pass without shipping, he has broken his standards HE set on himself. Of course sellers are human and things happen, but it sounds as though he has no good excuse for it.
Anyone who closes a dispute after opening one without the seller following through are screwing themselves out of money. I am a powerseller on ebay, been selling since 2003, so I know the ropes. My handling time is one business day and sure, sometimes it takes me an extra day but when it does happen, I message the buyer and explain why and also upgrade to the next fastest shipping service on my dime to make up that day.
The seller you got may just be having a bad time in their life, but there is no excuse for the threat after opening the dispute. If is unprofessional, and if I were you, I'd let them know compensation for this delay and unprofessionalism is in order to satisfy you. They brought it on themselves and should not get off the hook just for finally shipping the item days after they were supposed to.