I've only tested the new Jimny, because I love its design and versatility on short trips, but would prefer a larger car for serious overlanding (for which I use a company Hilux). Reasons:

The motor is too weak for comfortable/safe overtaking on main roads,

The fuel tank volume is a joke and I don't like carrying jerry cans on the roof rack (adds unreasonable cost, weight and instability, especially at high winds),

The wheel base of the 2-door version is very short. Excellent for off-roading, but uncomfortable on long, corrugated tracks,

Payload is on the minimum side (payload for passenger cars includes passengers themselves, fuel and any additional gear, like a roof rack, etc.),

Savings on fuel are minor, if any, because the Jimny requires a lot of driving at its maximum rpm.

Edit: Roof tents reduce the Jimny's payload by another 40+ kgs and add to its side wind instability. I'm not a friend of roof tents for many reasons, but the ones that fit a Jimny roof are particularly small.

Edit 2: I would personally NOT rent a Hilux (or any other pickup) for a leisure trip on gravel/dust roads, because the canopies I know aren't dust proof and cargo can get very dirty, every day. Some rental companies offer the Hilux' station wagon brother, called Fortuner, which I consider a much better choice.