I have had no heel issues with my Hybrid and panniers, and I don't think with my trailer either.

However, my other bike is a vintage racing road bike with short stays, and I have to be very careful with pannier positioning, and also typically choose triangular bottom panniers, rather than the rectangular bottom panniers that are becoming more common now. Perhaps my new rack also sits a bit further back on the bike than the vintage rack.

I'm not sure about aggressive vs relaxed fit of the hybrid. Some will depend on the actual frame chosen, as well as the ultimate build design including the stem and seat types and positioning. My "vintage hybrid" frame may well tend more towards the road bike styling, other than the sloping top tube.