Ipv4 TLD exhaustion happened in 2011, but it was functionally impossible to get a public IP directly from IANA closer to 2005.

And the routing would be a nightmare because if you have multiple gateways between non-overlapping CIDR ranges, you need to tell routing equipment how the packet should return to its source.

So ignoring there being no reason to expose sonarr or radarr to the public at large in the first place, you would be working with two potential scenarios with multiple IPS: either you have two distinct subnets blocks behind your gateways, or you you have two gateways to a single subnet.

In the first case, you would have to route traffic between the two subnets, which makes the scenario not make sense, because why would you need packets between two local hosts to pass through their gateways through public space when they could just be in the same subnet. In the second case, you would have to specify to all your internal hosts two gateways so traffic know which public IP to return to.

Neither of these scenarios make sense when NAT is a much simpler (and cheaper)solution.