The Japanese language does have tone accents which do distinguish meanings. Although context will sort things out in all but extreme cases, improper tone is one of the primary markers of a non-native speaker. Perhaps Japanese grammar is complicated compared with Chinese or Korean (I wouldn't know) it is certainly far more regular (ie easier) than European languages (like English.) Now the writing system on the other hand...
All in all, it probably takes the same amount of effort to learn either eg English or Japanese as a second-language.
No. You need to study/speak a language like Mandarin to really appreciate that tones are fundamentally different that merely pronouncing vowels differently or having an accent or conveying mood (occasionally). English speakers might pronounce 'tomato' differently between the US and UK, might raise their voices at the end when angry or yelling, Japanese might "swallow" a trailing -u, everyone might have a regional accent that pronounces words "funny" compared to elsewhere, but none of that is tonal in the sense that Mandarin is a tonal language.
In Mandarin, tones are part of the correct pronunciation of a word. Different tone = different word. As in "shi" with a rising tone can mean "10" and "shi" with a falling tone can mean "vision" and "shi" with a neutral tone can mean "poem". Japanese and English are not like this.
Yes, somebody with a US southern drawl may pronounce ten, the number, close to tan, the color, but that's a regional access a not a tone. Somebody emphasizing a syllable or raising the voice (mad or asking a question) is also not a tone - it is not part of the correct pronunciation of the word.
Japanese grammar is more complicated that English or Mandarin in a few ways (I don't know about Korean, I never studied that language), but at the same time it is highly regular. One example is verb/adjective conjugation. In English, if a car is red or was red, the adjective "red" stays the same, present or past tense. Similarly, in Mandarin, the chejì would be hóng, same word form. In Japanese, the kuruma would be akai or akakatta (or akakunai or akakunakatta to complete the conjugations). On the other hand, there are basically 2 kinds of adjectives in Japanese (-i and -na) and they follow fairly regular patterns with only a handful of exceptions.
English is complicated because so many words have multiple meanings, wildly different (spring as coiled metal, a season of the year, jumping) so almost everything requires context to decode, it is highly idiomatic, has a large number of exceptions to almost any grammar rule from conjugations to pluralizing and so on, pronunciation is a crap shoot with general rules about sounds and again as many exceptions as their are rules. One thing about Japanese and Mandarin is the pronunciation is consistent (and you start by studying pinyin or hiragana/katakana) even if it is difficult.