MTB guys do something similar. Wide, aggressive tread up front and narrow, semi-slick rear.

It's much easier to control a rear slide than a front slide, the way I see it. I personally run a different front vs rear tire even on the road. Road and gravel tires are going to have to start developing front and rear specific tires in the near future if we want to see improvement.

I wouldn't be so quick to conclude that you're sacrificing grip with the knobby front. You also have to account for things like compound, hysteresis, slip angle, progressiveness etc. that might actually make your knobby tire more forgiving at the limit.

In short, I agree with everyone above. The biggest downside is probably that your knobby front won't last nearly as long as a slick. And obviously rolling resistance.