Tonal was an ambitious project, and the results it produced were both engaging and frustrating.
It was engaging because it's practically a new game, with a completely fresh and interesting environment, and great sights for combat.
But it's frustrating 'cos it's so slow.
Yes, part of it is the sheer number of object on the island. But it's more than just objects. The map itself (24.6x24.6km) is double the size of a regular OFP island. The textures and the 3D models are all over what the "standard BIS" maps have -- the thinking was: "2 years after the original release, we should be able to have a higher minimum standard".
Then there's the AI: to encourage longer, "more realistic" firefights, the AI is given "high dispersion" ammunition. Firefights last a lot longer, and many more AI get involved in the slugfest. So when you have units in contact, the CPU load is higher -- not just from the bullets flying through the air, but from the calculations involved in all those AI that haven't died.
You can debate the logic of the "increasing standards" without resolve: one side will point to continuously improving computers; the other will argue that OFP comes with performance expectations regardless of addons. But the real frustration of Tonal is the pairing of a much-larger-than-normal battlespace with a requirement for far fewer entities in it.