You just answered your own question. 3 interfaces. 1 basic, 2 advanced, 3 luci. That means we would have 3 different interfaces to do things instead of 2.
I'd guess this is what the OP ment otherwise i just respond to re-occurences from past ui requests.
For the plugin section i totally agree it can be even removed because it is a advanced feature, and many get confused into updating them resulting into crashing, many times when someone needs a user package you are using luci or ssh anyway so, it won't hurt to remove it.
What i don't agree on, is removing the advanced settings, maybe it can be reworded, but this feature weights heavily why alot of people are interested in these products, without access to luci i don't see a reason to buy a router from this brand :), for me it is super unique what they do.
for port forwards and such, i think this is a normal feature which shouldn't be removed.
My only extra feedback to the ui:
more interopability, there is already alot support already especially for vpn policies (i mean it is more than it previously was, theres still some iptables rules going on) and such logic shown in luci in the firewall, but i'd still want to see wireguard being compatible with luci-proto-wireguard though that requires extreme lots of work, but will help the developers to aid more on other core features it means on the long run less work to maintain it, and it solves incompatibilities with other packages like banip, there is a chance it cannot detect the tunnel interface, but it would be if implemented like luci-proto-wireguard