I know a little bit about what Waltz is talking about.
The amount of "distance" from the native language to the learning language is important, as is the amount of cognates present. Other factors include word length (very long or very short words require more repetition since they are harder to fix in auditory memory / harder to distinguish in speech) and to some degree emotional involvement (drop the "f--" word accidentally in a classroom and see how many reps THAT one takes -- it's far below 50.)
8 to 10 revisions is nowhere near enough for a student to acquire a word (which means to have it firmly in the subconscious so it can be accurately output without effort or thought). I would really like to see Webb or anyone else teach new words to unconscious correct comprehension and production in only seven repetitions with beginners or intermediates. Most people are only figuring out which word is which at that point.
When we teach Chinese reading (which we do without pre-memorization of characters) we need a strong Chinese voice in the head to "push" reading comprehension since there is zero phonetic information available to novice readers of Chinese. You have to be able to "hear" the language in your head to read. That requires a lot of repetition. If you teach French, you need some voice because of spelling challenges, but the text will support you. If you teach Indonesian to English speakers, you need less voice still because the phonetics are very straightforward. If you teach Spanish, less still because in addition to very reliable phonetics, you have lots of cognates to fall back on.
So while it's true that in my experience teaching multiple languages, Chinese to English speakers requires more reps than Spanish to English speakers, the biggest divide in practice (and results) that I have observed in the past 30 years lies in whether the teacher stresses repetition -- which needs to be unpredictable repetition. Not "I can look ahead in the book" repetition, not "I know what the next question is going to be" repetition. And to generate that level of unpredictable meaningful language, usually you're talking about a CI (Comprehensible Input) based teacher. (I am NOT a TPRS teacher, though TPRS is one of the things I use. I teach using Comprehensible Input, or more correctly in my opinion, "Comprehended" Input, since anything that's not understood is noise to students.)
The more years I teach language, the LESS vocabulary I include, and -- counterintuitively -- the more proficient students become in the same amount of time. The reason is that they are getting more repetition of the same language elements, combined in unpredictable ways, over the same amount of time. Narrow and deep. But like Cold Character Reading (direct-to-text Chinese reading), which no one believes until they see it happen for themselves, Comprehensible Input is another one of those things that teachers dismiss until they experience it themselves.
I'm very surprised and a little weirded out to see people discussing me on StackExchange, though. lol