You guys should check your math, radius is center-to-edge, not edge-to-edge. You're thinking of diameter.
Following this, Brand's W would have a maximum range of 1150. Though, realistically, that's just a sliver and hardly any real room to hit someone.
Furthermore, Brand's full combo, including CC, can only be done from 625 range (E-Q-W), or 750 if he's using his ult.
Zyra's full combo, with CC, on the other hand, can be executed from around 1100 range, if you use the missile time to get in position for your Q. Her ult's radius is unknown, but at 700 range it's very likely that will be at least around 1000 range.
Furthermore, just going off pure range, Zyra's plants can spawn anywhere from 0 to 900 units away from her, with her guaranteed seeds from her W having 800 range. When activated by her Q, these plants can spawn from 800 units away, which then gain 750 range on their attacks, for a total of 1550 range (ignoring how generous the spawn area is). With her E, this range is similarly 1100 + 400 for the plants, giving her another tool with 1500 range. The only thing Brand can do that's similar is ult an enemy with 750 range, then have it bounce to another enemy, gaining an additional 750 range (1500 total). This would prioritize bouncing back to the original enemy, but if it was invalid or dead you could potentially increase the range by another iteration (2250 total) but this would be extremely unlikely and still require the use of a committed ult.
TL;DR you're both right, those two are f***ing annoying at long range.