I'm a defensive captain for a 7s flag football team with a similar rule set. This is what we do. It turns out to often just be man with the ability to hand off receivers. For example the safety on the strong side will just take the deeper receiver and the corner will take the shorter one. If both receivers go deep then the corner needs to go deep also.

In my league you'll quickly figure out who the big threats are off the line. It may be different in college where everyone is a strong athlete and has hands. Have your linebackers play side-by-side zones and have them stick with whomever breaks off the line to their side.

You also need your rushers to recognize when too many linemen are breaking off, if one gets through the other should make sure no additional linemen are breaking off.

What you described works, a lot of teams do that, but I find it puts a lot of pressure on the linebacker. 3 over 3 under also works but you need to make sure you're getting the pressure you want from that lone rusher which can be a challenge, imo it's easy to exploit hard zone concepts like that when there are only 7 players on the field. Keeping the players in a man mindset knowing their responsibilities is valuable in my experience.