True to a large extent. But as with any tool its usefulness depends upon the situation within which it is used.
Back in "The olden days" when I used iptables for the firewall for example. Using the commandline to check and adjust the rules and how they worked would involve a lot of time and fiddling with for example iptables -Lv then delete a rule and then reinsert it with a series of types commands and so on. With webmin a click to the iptables page, a rapid and accurate skim through the table and click on the up and down links to rearrange order. Nowadays, of course, it is even easier checking and amending the firewall, just typing nano /etc/nftables.conf brings up the whole set of tables ipv4 and ipv6 laid out schematically and easily editted.
That's just one example. For many tasks it is a bit of a pain getting it to do the things in the way that I want and anything to do with net interfaces or routes it is damn near impossible and the command line tools quick and easy to use. And again to use it effectively you do need to have an understanding of what is happening and how to do the things manually. You need to have an understanding of what is happening under the bonnet, obviously
You use it in situations and for tasks where it is more efficient to do it that way.
Having the repository in sourcelists.d Means that updating involves typing apt update followed by apt upgrade.

;-) Keith