I am Nodas from Greece. Excuse my English reply. But I cannot yet write in German, besides my basic reading/understanding of a few words.
I've been competing to the last 3 Mental Calculation World Cups ('10,'12,'14) in Germany and the last Memoriad ('12) in Turkey. I competed with Scott in Magdeburg('10) . To answer some of your queries: You said Scott's results 'were bad'. But from an insider's view I can tell you that Scott did not really try in 2010. I think Scott came in MCWC for social reasons mainly, like it happened last year when we met him in Dresden. It's a rare ability to have and I think also Scott likes to be among the best mental calculators, and next year he is the organizer of Memoriad 2016, which includes 5 calculation categories (Anzan included).
About Scott's real skills, he is amazing in 2-digit additions and especially in auditory recitals and in TV shows where it also requires social skills besides mental calculation. In my opinion, if Scott tried his best in MCWC, he could about in the Top-10 in addition and multiplication. Maybe he could also do well in Calendars week-days, which he also instantly calculates for 20th century. But I'm not sure how well he would do for other centuries. In shows he usually answers for 20th century only. However, in MCWC we compete in all years 1600-2100 and not only in 20th century. Besides that , MCWC tasks requires quick writing speed as well (even though only the final result should be written with pen/pencil). In order to find 52 calendar dates in Dresden, I was doing more than 65+ D1M in training/practice where it's more relaxed. To be able write about a number per second (for each weekday), while thinking, requires its own speed-writing practice, and it's not only mental calculation, but also rapid speedwriting.
But now it's hard even for us in MCWC; (I'm usually middle-rank competitor, my best overall place was 15th in Giessen'12 ) because nowadays so many good Indian kids come to compete and it's hard even for us adults to keep up with their speed. In 2 of the 3 MCWC competitions that I've been to, 2 first-timer (and previously unknown) Indian children, came and won the overall competition (Priyanshi (2010) and Granth (2014), both very fast). The standards are getting higher and higher, and in my opinion the winner of MCWC is the best 'competing' mental calculator in the world. I said 'competing' because in India or Japan or China there maybe other better mental calculators. (e.g. the Anzan guy you mentioned). But many of them, unfortunately don't the option of travelling and competing in the West. So, we can't really know, unless they come and compete.
In Memoriad, it's a different format. Only seperate categories are rewarded and in MSO in London, with all due respect to Dr.Dr. Mittring (also amazing and timeless) very few people compete there in MSO (about 10 or so). Thus, all these various mental calculation formats, are quite different in nature from the amazing recital speed like in Scott's TV shows appearances. There is no absolute measure of comparison. Granth and many others are faster than Scott, but Scott has proven incredible oral mental calculation skills in front of the TV camera, which is demanding task itself, given the pressure and anxiety to perform correctly. Every one, can admit Scott's ease and coolness , when he goes to demanding shows like Oprah Winfrey to show some mental calculations in front of millions of watchers.
The fact is, that Scott along with Mr. Arthur Benjamin, are the most known mental calculators in USA. Thus, it's nice to have such a big famous name like Scott in the real mental calculating community who competes in contests (MCWC, MSO and Memoriad). I think the mental calculating community needs not only people who write books or go to shows, but also compete. I wish other famous MC people like Benjamin or R.Gamm or Dr.Dr. Mittring could also re-join a unified competition (MCWC or a new one) , in order the have the best contest with more fame and status. Maybe such a contest could also advertise well in China or Japan in the East, where I think they also have a huge pool of mental calculators, whom we don't know yet about.
P.S.: Bottom line, the competition results don't always tell the whole story
Nodas, mental calculator from Griechenland
Current Greek National Memory Record holder for the Memorization of Pi/π
My MEMOCAMP page: https://memocamp.com/en/bestenliste/benutzer/8286-nodas