While English may not have a dual number, a case system (anymore, though it's still seen vestigially in the pronouns), or a verb conjugation expressing the future tense, the point is that English speakers are not constrained in what they are capable of expressing.
For the dual number, we simply say "two cows" or "both cows". To express the future, we have "will", "be going to", or a present (progressive) future construction like:
"We play tennis on Saturday" / "We are playing tennis on Saturday"
Whereas other languages use case to express certain semantic/grammatical relationships, English fills this void with word order and a slew of prepositions.
So at worst English speakers expend a few extra syllables on certain ideas. But there is no limitation on expression or cognition, which is the claim made by a strong version Sapir-Whorf.