Not an expert, but afaik there's been quite a few studies showing that natural immunity is superior to the vaccine-induced one - I'm also fairly sure that virologists have theorized to that end even before the data became available for the following reason: the vaccine is 100% focussed on detecting the spike protein, so changes to the spike can result in evasive variants. Natural immunity OTOH is developed against more sites of the virus and thus provide a more broad and robust response to variants, present and future.
There's been some mixed signals coming out of the research, but that's in part due to how immunity is being measured. There are definitely some studies showing that particular antibody levels for vaccines can be higher or longer lasting than natural infection, but recent research is showing that those with natural infection have had a far smaller risk of reinfection than those vaccinated, even when controlling for comorbidities. There are still confounding factors, such as behavioral differences between the groups, but its a pretty stark difference. It also makes sense from a theoretical standpoint, as acquired immunity is based on more than the just spike protein, unlike the vaccines, which is a big part of the differences between variants like Delta. The thought is that natural immunity is therefore more resilient to changes between variants.
Its all early enough that its still an open question, but there's definitely early evidence that natural immunity is more resilient than vaccination only.
