With all due respect, the very notion of any particular type of ear phones, universal IEM, full-size, custom, whatever, as being overrated can produce an interesting debate, maybe. But in reality, since metrics really are never part of this type of discussion (and I am not counting FR charts etc., which have limited use in my view), the entire issue is way too fraught with subjectivity. presumption and personal bias. Isn't it like asking if any other product that produces mainly a subjective experience but costs more (the driving aspects of a Corvette vs. a Porsche, for example) is overrated? I realize the OP is asking if high end customs are not worth their price, right? Because there are much less expensive products delivering basically the same experience. Well, that supposition is a losing proposition from the get-go. It just can't be determined. Debated, sure. But in the end, it is a definitively unanswerable question as long as someone (the OP, for example, and there are no doubt others) believes that high-end customs are, in fact, overrated.
I have limited experience with customs, having owned a single pair of actual ones (the JH5s) and one pair of pseudo-customs (W4s with UM56 sleeves). I have owned many many universals, and so far, none of them have matched the sound quality (as only I hear it, of course) of those two IEMs. For now, I have stopped buying "high end" universals. I am content. Along those lines, I recently owned the Sony EX1000s, which are the main driver behind the revival of this thread. In the end, I didn't believe the EX1000s outperformed the JH5s or even the "custom" version of the W4s. Just my view. I bought them knowing I had 30 days to return them to Sony with only the postage to send them back at stake. Small risk, potentially big reward. But in the end, I wasn't convinced. I guess I could say the EX1000s are overrated, but I won't.
Do I believe that getting a pair of Westone ES5s or JH13/16s are going to be an insta slam dunk winner over the JH5s/W4s? I have no idea. But in my view, there is really only one way to find out. Debating is all well and good, but in the end, what matters is what you have personally experienced - and even then it only really matters to you, and for you.
So my plan is to be content, for now. Then, at some point, I will maybe will try out a new, expensive custom IEM. Maybe even one of the new hybrid models that are popping up all over the place. I am not sure. If that purchase turns out to be less than satisfying (in other words, if that pair of customs is overrated based on the factors going into my decision, and compared to the JH5s or W4s), it still can't be concluded that high-end customs are, in general, overrated. That overall question/issue will never, ever be really answered by a bunch of people tossing out their personal experiences, it's just not gonna happen. Those views can help others decide, but in the end, again, the buy and try strategy is all that will suffice - just as it did with universals for so many HFers. And on a case by case basis, buyers/owners will decide whether or not they made the right move.
Oh, almost forgot. To answer the original question, do I think my custom IEMs are overrated? No, I don't.