i'd say mandatoryhealth insurance required by OA visa not quite useful as pre existing health problem are all excluded, so better opt for O retire visa which does not require this, besides it is not possible to change OA to O while in thailand, insurance premium will be very costly too as one gets older
i think the main poblem is that all pre existing health problem are excluded.from protection but you are most vulnerable because of these pre conditions
elite visa probably needed if you can not find other ways to get a long stay visa, like you are too old to get mandatory insurance or simply too costly