Actually, the comparisons are not quite right.
You are aware that modern helicopters are powered by jet engines, right? They have been for over 60 years now.
But there is just as big of a difference between a howitzer and a tank than between any other vastly different pieces of equipment.
Would you confuse this with a tank?
Because this literally is the same thing. An 155mm howitzer. The other one simply has it's own chassis to drive it around, instead of having to be towed. And I do mean that literally, it is the exact same gun. They just drive themselves, and can be emplaced and roadmarched faster.
However, as they have a limited number of rounds with them they are more used in a mobility phase of an operation, and are not as flexible as the towed variants.
However, as they are indirect fire weapons, there is a huge difference (without counting the armor and that they can be fired on the move) with a tank. As tanks are direct fire weapons.
In fact, the Howitzer has more in common with this:
Than it does with any tank.