Ah ok, so you don't think they'll last longer if you leave both ETA and Miyota unserviced, just that it's superior in terms of cost saving. I agree, swapping out affordable reliable movements does make a lot of economical sense. It's why I love NH35 in anything <$500.You're putting words in my mouth. Additionally, you're adding your own value judgments and bias to the comparison.
The ETA has a long track record of being reliable - WHEN IT'S SERVICED ROUTINELY. By comparison, the Miyota 9's are a dozen years old, and no one is having them serviced, because it doesn't make sense to service one when it's cheaper to just replace the movement, and no one would do that if it's still running well.
I'm just looking at these things logically, using the facts I have available to me. I'm sure you've seen me explain the logic already, but I'll explain it again.
I've spoken to at least a dozen watchmakers about this. I ask them all the same questions about Swiss mechanical movements. Among those questions, I ask them how long the service interval really should be, because I've seen that debated endlessly online.
Their consensus is that you can stretch that interval out a bit if you're not wearing the watch every day, but even if that's the case, it really ought to be serviced by the 7 year mark, because the lubricants dry out, and there are likely to be parts in need of replacement. Delaying beyond that point is likely to do more damage to the movement, increasing the inevitable costs when the watch is eventually serviced.
To be fair, service costs vary, it seems, with location. I've seen people say they can get a movement serviced for $200 or less, but I've never had a watchmaker quote me a price that low. The lowest was never less than $300, not including the cost of any parts which need to be replaced. That also doesn't include any shipping cost, if there isn't a watchmaker within a reasonable driving distance.
You can buy a standard grade ETA 2824-2 from a supplier for about $200, including shipping. If you know how to regulate and do movement swaps, then you could just replace the movement yourself, for less than the cost of servicing one. Even if you don't know how to do it, a watchmaker might agree to swap a new movement in for an old one, but I'd bet your total cost would work out to be about the same - around $300, for the cost of the movement, and the watchmaker's time.
So, you're looking at ~$300, maybe more, whether you service or replace one of those movements. If you want to wait until the movement dies before you do that, okay, then wait. But while you're waiting, you're likely going to see a drop off in performance - decreased accuracy, and maybe decreased PR.
How does that compare to Japanese movements like the Seiko NH3x's or Miyota 9's? We say just let them run until they die.
Replacement cost? $40 for the Seiko NH3x. $100-$120 for the Miyota 9's. Swap the movement out yourself, or pay a watchmaker to do it. Even paying a watchmaker, the service is the same, so the lower movement cost means it'll be less than what you'd pay to replace a Swiss movement.
What happens while you're running them until they die? Maybe you're seeing decreased performance. But when does that start, and how severe is the drop-off?
The Seiko NH3's (7S35) is a successor to the NH25 (7S25), introduced in 2004. There are tons of 7S25's and older Seiko calibres out there, still running well without ever being serviced, some for decades, like my old Seiko Pogue (now 50 years old, and still running well). The Miyota 9 series was introduced in 2009, more than a decade ago, and we haven't heard of massive failures in the meantime.
Can we say for sure what will happen with the NH35 or Miyota 9 series in the future? No, but when we look at the longevity of other Miyota movements, like the 8215 (introduced in 1977), and all the vintage Seiko and Citizens running well without being serviced for decades, and we look at how robust and reliable the newer calibres are, I think it's reasonable to expect these newer calibres to also be maintenance free for decades.
I don't think any reasonable person would truly assume this, but if we want to be absurd, we can worry that the Japanese movements will need to be serviced or replaced just as often as a Swiss movement should be serviced or replaced - no less frequently than every 7 years. Okay, assuming the worst, the cost to replace one of the Japanese movements is still going to be less than the cost of servicing or replacing a Swiss movement.
So, in that way, I think it's fair to say the Japanese movements ARE superior, at least in terms of long-term ownership costs.
Loads of Swiss movements left unserviced for decades that still tick along (I know loads of people buying Swiss watches don't even know the concept of servicing). I think people expect this when paying for Swiss, but you hear more about Japanese lasting long because they are much cheaper and perhaps surprise people. I don't think one is significantly better than the other when it comes to unserviced longevity.
The cheapest you've seen for a service is $300? My only Swiss mechanical movement is in a Stowa (2824Top), and they charge €190 ($230) for a full service inc replacing parts. I don't wear it as a daily so might service it every 10 years or so...~€20 a year, really nothing to panic about.
If I did have something worth, say, $700 with an SW200 inside it, I would probably treat it like a Miyota and run it to the ground and then perhaps even replace it with a PT5000 (or whatever solid ETA2824 clone is on the market at that time).