IMO studying the history of any subject, you're interested in, is really useful as it helps understanding why things are the way they're in the present.
Now, regarding the subject of the 'history of philosophy', what are the contents and how they're structured is a different kind of problem. And, unfortunately, it's not limited to the 'history of philosophy' as we face similar kind of challenge when studying other important subjects.
This challenge can't be avoided all the times but needs a systematic approach; otherwise, one might easily commit the (proverbial) mistake of "throwing the baby out with the bathwater".
Now, regarding the subject of the 'history of philosophy', what are the contents and how they're structured is a different kind of problem. And, unfortunately, it's not limited to the 'history of philosophy' as we face similar kind of challenge when studying other important subjects.
This challenge can't be avoided all the times but needs a systematic approach; otherwise, one might easily commit the (proverbial) mistake of "throwing the baby out with the bathwater".