To say it's less powerful than "plain PHP" is just wrong, since via custom modules, which you'll be writing at least a half dozen of for a real non-trivial (e.g. the kind of thing you wouldn't just do in WP, just you can essentially just sprinkle in 100% custom "plain PHP" whereever you need it, while still being able to leverage things Drupal does right, like form handling and batch operations.
I ultimately found that I was happier writing stuff closer to the way wordpress does it.
It really comes down to two things
1. depending on what tools you have available, what you are familiar with or what you are capable of understanding .. drupal or wordpress might be easier for you than the other. That's relative.
2. is the fact that the wordpress model is objectively simpler than the drupal model (at least last time I looked, around 4 years ago).
So I'm not saying one is better than the other at all, just that this is how they are different.
If you know, or are willing to learn, a bit of code, wordpress is most likely subjectively easier than drupal would be.
We actually didn't use Drupal forms for much on the front end (The occasional webform for user submissions, etc, but very few actual drupal api forms), but on the admin backend we had lots of little things I threw together that worked well but were not used all the frequently (and then only by power users).
Our frontend was primarily done through a system I called the Page module (Because it was the module that made...the pages - for instance http://www.reflector.com/news). That was actually a really cool hack. It worked a lot like views - but could actually run on a high traffic site without bringing the whole thing to it's knees. The trick was that the really nasty join across about 8 tables (node, the content type data, related image data, story body (for teasers), and a couple others) was done only on node save and that was stored in an index table (not everything on the node, but just what I needed to build a page). So to generate each news block was a really super simple query of basically:
select * from page_index where page_blockid = 12345
order by updated desc limit 5
instead of something like, and this is the super simplfied version
select * from node left join content_type_story cts
on cts.nid = node.nid left join taxonomy_data td on
td.nid = node.nid left join uploads on uploads.nid = node.nid
left join upload_files uf on uf.uid = uploads.uid
left join node_content nc on nc.vid = node.vid
where (td.termid = 1231 or td.termid = 1256) and
node.published = 1 order by updated desc limit 5
Of course, we were running multidomain so a lot of those tables where domain alises etc, again, all precomputed in my module.
No, I don't miss it. But it was powerful, and I did develop, deploy, and serve 3 daily newspapers with 20k+ circ each with a dev and sysadmin staff of 1. There is no way I could have done that if I'd had to write everything from scratch.
To put it another way: the fact that you can greenspun Lisp in C doesn't mean C has all the power of Lisp. It means that Lisp has all the power of Lisp. Every even-mildly-useful language is Turing-complete; so, in order to be able to give a ranking to languages at all, we have to restrict our discussion of a language's merits to its merits if you aren't just using it as a glorified Turing machine for implementing a different language.
Without writing custom PHP, Drupal is less powerful than PHP. That's perfectly okay.
http://en.wikipedia.org/wiki/Inner-platform_effect
DSL's are generally not turing complete. When they are, they tend to look more like lisp.
Also, Drupal is NOT a DSL, even in the way, say, Rails is.
The original assertion was that Z was more powerful than X, and I merely stated that that is false because X is really the superset X+Z, whereas if you are using JUST Z you don't get X.
We're not talking about 2 different languages here.