`nftables` may have replaced `iptables` but I don't know it from my current Debian router - my complex `iptables` firewall and routing script runs great.

`ipchains` was replaced by `iptables` in the early 2000's I think.

Also I got `isc-dhcp-server` running and kicking just fine. And straight `bind9`. I know `systemd` does both of these but nothing's forcing you to replace it-at least on Debian anyway.