your going to get a biased opinion, but for me,the ocean has built in chairs,outdoor table. built in heating,factory roof (not cut open a van) 3 zone air con (not seen many conversions with that), top loading fridge (access with bed down,unlike some conversions you can't get the fridge door open with downstairs bed made up. kitchen behind the passenger seat gives unlimited driver seat adjustment where as conversion kitchens are all behind the driver. usually higher power engines (some convertors use 102ps base van. proper awning mounts bolted into the roof (some conversions i've seen them rivetted to the van body,and without a rain seal. gas bottle built into the water tank and sealed with factory gas drop out. more storage in the boot. i'm sure theres more i missed.
a mate of mine paid 30k for a van and another 30k to convert it,that doesn't make sense to me either,plus can have insurance issues.
the only up side i see of a conversion is you get bigger range of colour options and can have a lwb for more room.and if it really bothers you the sliding door is on the other side,but unless you camp in p1ssy litter strewn laybys thats not an issue.
good luck in your hunt,
god i'm bored today. lol
edit,not owned a conversion