I think inconsistency is a frequent problem in magic systems, especially since fantasy writers tend to go for long series, and the needs of the story may "outgrow" the original magical rules.
It bugged me in the HP books that one of the cardinal rules was you couldn't (truly) bring someone back to life once they were dead, yet you could turn a teapot into a perfectly good turtle or a pincushion into a hedgehog that felt pain (there was also that thing where no one seemed to care in the magical world about torturing and killing animals as spell practice, even though the contemporary muggle world--where no one can actually talk to or turn into an animal--had/has pretty strict rules in place about when and how one can use animals for educational and research purposes, and even rules for treatment of food animals are getting stricter), or a teacup into a hamster that was real enough to be a child's pet after. Surely if you can take inanimate matter and organize it's molecular structure into a living, metabolizing, feeling creature that behaves normally for one of its kind (so it presumably has a all the thoughts and feelings and memories it should possess as an adult member of its species) and presumably has a soul and all that given that souls are presumed real in that universe, reanimating a corpse would be a simple matter. Also, how is it no one ever thought to turn something inanimate into a human? Humans are animals, after all, and they are not fundamentally more complex on a cellular level than any other creature (and even if human memory and intellect are harder to create from scratch, some evil mage with a god complex wouldn't mind producing a human, even if that person turned out to have the mind of a baby).
I wouldn't call the magical system "terrible," though. Some of it was quite clever and whimsical, and the HP books were written for kids. She did have limitations and risks built in as well. Still, some things did go unexplained, such as how Harry could use his wand to read his spellbooks under the covers at night when at the Durselys', yet the underage magic folks were able to detect a levitating pudding. I'm sure there are HP fan forums somewhere where people discuss these things at great length and posit potential explanations.
I agree that Brandon Sanderson's explanation of magic systems and the "hardness" or softness" of their rules is a good one.
In general, the more the plot relies on the application and use of magic by the main character(s), the more important it is for the rules to have a certain amount of transparency. In books like LoTR, where the protagonists were non magical, and magic was either an obstacle to overcome (when wielded by antagonists), or an occasional thing used by very powerful characters but not understood by the protagonists, more opacity of the rules works just fine.
I'll admit to a bias towards magic systems where the magic itself is more limited, and its power and utility stem from very specific ways in which it can be wielded. Stories set in worlds where magic percolates every single aspect of life can be fun, but I find it hard to take all the "ripple effects" into account and imagine what such a culture would really be like, so if the story needs the world to be somewhat like ours in terms of how most people live their lives, then having spells for every trivial purpose doesn't work all that well.