I just want to share my not-so-extensive-and-average-guitarist experience with both asian and U.S. pickups on this topic even though I virtually don't know anything about the process or materials in making a guitar pickup. I have 3 electric guitars and have used 4 kinds of pickups. 3 of them are stock pickups and 1 after market Seymour Duncan SH-4. My guitars/pickups may be not worth mentioning for some but for me they are:
1) Raon guitar with Generic Raon pickups, made of $%#& wood (LP shape). The owner of a local recording studio in our neighborhood back then described the pickups as "fake humbuckers" because apparently inside the pickup cover is just a single coil and the cover was attached to make it look like a covered humbucker. It was "okay" for me. Namimili siya ng amp. Minsan maganda minsan hindi, but I get by with some amp simulation sa zoom g1x ko noon. At pag heavy distorted ang gusto mong tone maingay at mafeedback, hindi ko magamit. My main problem during this time was feedback, I even tried putting foams inside the cavities of the guitar. From clean to crunchy medyo maganda na. I played mostly RHCP and to my ears I can get it with the right amp. (Of course not really nail it we all know that's difficult not to mention possibly impossible, but nakakaenjoy naman pakinggan hindi yung tatamarin ka nang maggitara kasi ampanget talaga)
2)Same Raon guitar with SH-4 pickups. It was really an improvement. Like someone said here, somehow "it gave life to a lifeless guitar". The feedback problem was dealt with and I can use much more distorted settings. (This time I don't use multieffects anymore with amp modelling, just a dirt pedal)
3)Greco EG700, 1978. After my raon guitar was rendered useless, (not the electronics, the guitar itself because it was really made of $^&* wood), I acquired this Greco guitar with its stock pickups (U2000. I think it is right to assume that this is also MIJ same with the guitar, hence asian.). I originally planned immediately replacing the stock pickups with the SH-4. But after asking advices from some people, I decided leave it as is. I was beginning to play blues at this time and until now (it's been 2 years) I really like what I'm getting out of this guitar with all stock electronics. The SH-4 was really good even though I've used it with an averagely crappy guitar. I'm not planning to replace this guitar's stock pickups simply because I like how I sound with this and it's great for what I use it for.
4)Yamaha SG-200 with stock pickups (Either Made in Korea, China, or Taiwan I forgot, but it's just either of the those 3). This guitar sounds brighter than the greco but warmer than the raon made. Even though the pickups are humbuckers, (I've read in some sites that some people swear to only use single coils for funk, esp. rhcp style, because we all know it, from hillel to josh, they all mainly use strats) I feel good using this guitar for funk because of how it sounds and because of the feel of its neck. Mas nakakapagexperiment rin ako dito kesa sa greco LP ko parang dedicated lang ang sound niya.
Sorry if I'm off topic, napa-share lang haha. One should not base their option on the makers alone. Dapat ma-consider din ang guitar na paggagamitan at kung swak sa gusto mong makuha. Baka naman hindi pickup ang problema.
Bottom line of my lengthy narrative is that my asian pickups deserve more than my attention.
Palagay ko sa ibang MIM guitars sinasadya na mas mababa ang quality ng pickups kesa sa "higher end" models (Marketing strategy maybe?) but if it gets the sound in your head then why not. Maybe I'll try Mang Max's pickups when I make my project guitar.