I think the restaurants landside at KIX are fine and there are plenty of choices. Sure you won't get a real Japanese experience like eating at a locals sushi joint, but your time is limited.

As for three hours...you'd better hope that you inbound flight is at least on time. Remember you will have to pass immigration controls twice as they have controls when leaving the country too.

However, I have found KIX to be less and less busy in recent years. I think many international carriers no longer fly into KIX (for example, Air Canada my home carrier no longer flies to Osaka - which sucks b/c that is my wife's hometown).