Translation:Don't you think that a billion is too much?
I disagree, I think it's often not necessary in writing as well (see what I did there?).
I wasn't able to find any sources that supported your opinion after a cursory check, but here's one that supports mine: https://www.quickanddirtytips.com/education/grammar/when-to-leave-out-that
Another problem with this translation is that it accepts "a billion" but not "one billion".
Should be accepted, but:
Too many - when you talk about an quantity (discrete)
Too much - when you talk about an amount (continuous)
you won't say "too much people" but "too many people", and on the other hand, you won't say "too many water" but rather "too much water". So that being said - I can't think of a situation where you count a quantity of something in billions, it should become an amount way before.
I agreed it should be accepted. And yes, some nouns are countable (many people) and others are not (much water). But the grammar in English doesn't change when the numbers are large. If there are 7 billion people on earth, that is 'many people', not 'much people'.
Billion is a number. Hence the correct term is "too many". Much applies to amount, not number in English
Money is a collective noun. We could not say "too much dollars" but would have to say "too many"; on the other hand, we could not say "too many money" but would have to say "too much". Therefore, a billion could be either too much or too many, and BOTH should be accepted. A billion is too many dollars or a billion is too much money!