Quality control, fit and finish are far better with ESEE. Many Ontario Rat knives are still around, and good knives. Like any other Ontario knife, at least mine, you might find the handles aren't perfect, might be boxy, or uncomfortable during hard use. You may get uneven edge grinds, and a so-so sharp knife.
With Ontario you will save money, they keep their prices low. The sheaths are another reason they are less expensive.
ESEE knives are sharp, strong, the handles are fitted to each knife, very good sheaths, many options for colors, sheaths, serrations, and the grinds are perfect. Don't forget about the awesome warranty.
The ESEE5 is very thick, you won't break it. I don't feel that it's the best for bushcraft. The 3/16" thick knives are fine for the uses you describe. Don't abuse the knife, and it won't break. All knives get dull with hard use, depending on the heat treat of the steel.
If you want a 1/4" thick camp knife, look at the BK2 from Becker. It's grind starts much higher, so the edge is thinner, and will cut wood, and food better. Notice the difference in the pic...