Blaine County was the standard for rural GTA-style areas: Sandy Shores, Paleto Bay, Grapeseed, Mt Chiliad. Leonida's rural areas have a different flavour. Here's how they compare.
Geography
Blaine County is all desert/mountain. Leonida is all wetland/flatland. Varied terrain means varied gameplay. Exploring Blaine focused on heights and dirt paths; exploring Leonida will focus on water and saw grass.
Density: Blaine was sparse on purpose. Based on trailer aerials, the rural regions of Leonida could be denser - more visible buildings, more visible bustle.
Towns
Blaine featured Sandy Shores (trailer-park-coded), Paleto Bay (small-town-coded), Grapeseed (farming-coded), and a few micro-settlements. Leonida's named-town situation remains to be confirmed, but trailer aerials suggest a similar pattern.
It remains to be seen if Leonida's small towns can hold a candle to the memorable side content Sandy Shores had to offer.
Gameplay vocabulary
Blaine: off-road driving, hunting (limited), Mt Chiliad mystery hunting. Leonida probably has a vocabulary covering airboat driving, beach side-content, maybe fishing, maybe hunting.
Various flavours of rural gameplay; same broad archetype.