Another really not nice thing about Mandarin is that its phonemes are generally less redundant. Let alone the tones, there are lots of consonants to distinguish, and in general, the average syllable contains more information than in other languages (Spanish or Hawaiian at the extreme end). So any noise in a communication channel, or a not-so-experienced speaker and it's unintelligible. That's also one reason why Mandarin still uses Chinese Characters. Especially with dialects, native Mandarin speakers can have trouble understanding each other.
Arabic has some of the same problems, if less pronounced, but its strength (in my opinion) was the reach of standard Arabic as written and spoken language of a major Religion, and it was/is used as trading language.
Latin was very good at assimilating foreign words. Again, it was the language of an empire and of a state religion.
I won't say that the success of English is only due to its linguistic advantages. Clearly, the cultural dominance of English speaking countries has helped. But still, it's a lot easier to learn than most languages, especially for people from indoeuropean backgrounds. Even for Chinese it seems to be easier to learn English than learn to write Mandarin to a high proficiency.
That's why I don't believe Mandarin will dominate over English, not even in a distant future. And there just is no other contender to the throne. The most likely alternative would be something that evolves from English, but with the current language being preserved in the cultural permafrost of books, movies and the internet, that's going to take a while.
This is compared to English or most Indoeuropean languages were you copy the term unchanged most of the time.
Just a minor point. But it makes learning the terminology of a subject rather hard.
You likely come (as did I) from a background in which such languages are quite unfamiliar but that doesn't make them harder or easier in general. John DeFrancis wrote a funny essay about the "Japanese plan to replace the Roman alphabet within their empire after conquering North America" as a parody of the people who think that the Chinese and Japanese should replace their writing with an alphabetic approach.
You may not realize how hard it is for many speakers to learn English spelling where spelling is more conservative (to preserve meaning) than more phonetic writing systems like German, Spanish, Korean etc. The terms are seemingly more obscure. In fact it's to reduce that problem that we violate English "rules" to conserve the declension of the original noun (e.g. felid/felidae) which is uniform when the term is a loan word common across languages.
It's also an objective reality that it takes more pieces of information to learn the Chinese representation of an English term than the other way around.
It doesn't mean learning English is always easier than Chinese, though it actually is for maybe even most Humans on earth.
Ignoring path dependency the same could be said of English. And while that path dependency provides hysteresis, it doesn't imply inevitability; Arabic and Latin had good runs as dominant scientific language but were eventually overtaken by English, which will ultimately be overtaken in turn.