> but are those mutations antithetical in some way to antibody production?

The problem Delta presents to antibody-based protection is that there is a several day lag in the body's response to detecting the virus until it produces mass antibodies.

If the (small) number of circulating antibodies are overcome by a large viral load, and if the virus becomes transmissible in a shorter time period, it can "get inside the curve" of antibody response and result in a transmissible infection before the host mounts a full response. Delta is apparently a couple of days 'faster' than the previous Alpha strain in getting to the transmissible stage.