You can counter that it isn’t like chanting because we aren’t using sounds or words with the idea that these hold power in themselves. Compare with Buddhist or Hindu chants, which are sometimes unintelligible, are believed to hold spiritual and psychological power, and/or can go on for hours. This isn’t meant as an “us vs. them” thing, it’s just to see the difference.
Rather, the rosary is a meditation on certain events of Jesus and Mary’s lives by means of reciting certain prayers. As for having a biblical basis, you can answer that the rosary per se does not have “biblical support” but the events being meditated upon are indeed present in the Bible, specifically in the New Testament.
Regarding your other question, Protestants do actually say the “Our Father” but perhaps a slightly different version sometimes (for example, using “debts” and “debtors” instead of “trespasses” and “those who trespass/trespassers”) with the doxology added.
Hope this helps!