Nice thing about potentiometers is they work up to low GHz (for the small, single turn, SMT ones with simple tracks).
If you need ppm with respect to code vs. frequency, you're probably not going to get it with this part even at 10kHz. It's not clear if that's quite the spec you need.
OTA = Operational Transconductance Amplifier, typically used as the core of a VGA or (active, single or double balanced) mixer. An LM13700 wouldn't give you the bandwidth here, but there are faster types. The main downside is temperature sensitivity, usually compensated with a PTAT thermistor (or sensor + lookup table). You'd probably not get ppm stability that way.
AFAIK, the traditional way these days is digital scaling, into a DAC with enough bits and sample rate to do the job. Analog multipliers have always sucked, there just wasn't anything better until the last few decades (depending on what kind of thing you're talking about, from audio synth to RF).
Hell, what are you doing, anyway? If that's low ppm's, it's not even meaningful without a 24 bit DAC, and 1MHz isn't very meaningful at 24 bits!
For a standalone adjustable attenuator sort of block, a chain of relays in binary dB steps (i.e., 40, 20, 10, etc.) is hard to beat.
Tim