"Whereas you going down"? If you're going that route (creating a second independent clause), the gerund needs a helping verb: "whereas you are going down". I assume that's what you meant anyway.

Come to think of it, I guess that's why "whereas" and "while" wouldn't work here: they have to connect two clauses. "you down" doesn't have a verb, and therefore isn't a clause, and therefore defeats the criterion for using "whereas"/"while". But "and"/"but" don't have this restriction - the verb is optional for them. (And for all of these, the verb can be in either the simple or continuous present)

TL;DR: course creators, all of the following are correct:

• and you down

• and you go down

• and you are going down

• but you down

• but you go down

• but you are going down

• whereas you go down

• whereas you are going down

• while you go down

• while you are going down

...but the current sentence is not.

It also sounds most natural to match to tenses - if the first clause is in the simple present, the second clause should also be in the simple present; if the first clause is in the continuous present, the second clause should also be in the continuous present. In my opinion, the best translation is We are going up, but you are going down. This is probably the most natural option.