PgAdmin does handle these functions, but the UI can be buggy, and is subject to problems with slow network connections - forced restarts can be common.
Making object editors takes a lot more effort, especially considering all the different objects PostgreSQL has: schemas, tables view, materialized views, indices, functions, sequences, etc.
I'm struggling with this myself. I'm currently trying to add object editors to PG Commander, and it's months and months of work. I wanted to have a table structure editor in PG Commander 1.0, and now, more than a year later, I'll finally be able to deliver a basic table & view editor in version 2.0 -- you can try a prerelease here: https://eggerapps.at/pgcommander-prerelease/
The latter is where PgAdmin is most useful for DB objects. The DDL view not only shows me things like CREATE TABLE/VIEW/FUNCTION etc., but also shows dependent objects such as constraints, indexes, permissions in the same window. Most of the JDBC based tools do not.
Graphical explain plans can be very nice to have, along with status views that make things like pg_stat_activity easy to consume in an actively refreshing compact view.
[1]: http://sequelpro.com
Although this tool, 0xDBE, doesn't look to have any DBA features like the OP was requesting.
Plus the two things are not contradictory. You can do them in the GUi and get the resulting SQL / DDL code to automate them later.
And not every database in existence is part of a larger stack. I don't care much about automating a task I'll only do once in a throwaway DB that exists only on my computer.