let me start by saying i think there are multiple layers to zoro's character, but becoming stronger (his dream) is obviously the most important part.
mihawk had an insane introduction. the fight between him and zoro is amazing because it showed us the immense gap between zoro and the strongest swordsman in the world. honestly, this fight is what really got me into one piece at the time, i wanted to discover the journey zoro would go through to finally reach that level.
mihawk doesn't need to be a "compelling" antagonist in the way you mean. zoro wants to become the strongest and to do that he needs to surpass the current strongest, it's simple, but it is enough and not underwhelming in any way.
shiryu will be a significant obstacle on zoro's path of becoming the strongest (i think the 2 sides of swordsmanship presented by koushirou and kozaburo might come into play in their fight), and i have no doubt he will be a top tier (most likely a conqueror), but mihawk needs to be the ultimate obstacle, the current "king" of swordsmen that zoro will have to dethrone (to me this is what chapter 1033 implied). mihawk hype is crazy and we didn't even see him all out yet, zoro defeating many strong opponents before mihawk only adds up to the hype, and i think it should stay that way. zoro -> obstacles adding hype to mihawk -> mihawk the ultimate test. mihawk words to zoro in their first fight are really important.
sorry if this was worded poorly, i didn't have that much time to write this and my english is not that great.