Netplan has oversimplified things to cater only to the simplest of topologies. The schema seems unable to capture the richness and modularity of actual networking technologies.
If by "only the simplest of topologies" you mean: 4 physical interfaces, bonded with active/backup failover and mii-monitoring, and 20 VLANs, turning off IPv6 on my public interface...
Honestly, I really like netplan, been using it for all my systems for ~5 years now.
I was able to set up fiber link aggregation with triple NICs and a custom VLAN and MTU with no issues. It supports bridges and child interfaces just fine.
I've achieved more reliable and reproducible complex setups with netplan than any hodgepodge of ifupdown scripts has ever done for me. Which topologies does it not work for?
Linux allows you to bind a subnet of addresses to an interface so that an application can listen on them. The netplan syntax is poorly thought out and overloads the CIDR notation to specify both the IP and netmask, so it is impossible to specify more than a single address.
I use this functionality in production for high availability configurations and effectively have to have a cron job to use 'ip' directly to fix things up.
Honestly, I really like netplan, been using it for all my systems for ~5 years now.