So if I understand this correcly, I can calculate the rpm using the equations you gave me from the wind speed?
Yes, exactly as I said. The cups are designed to give a linear response with wind speed and so you just count the revolutions. If you want high accuracy on speed then there is a secondary correction you can apply, but that's a different topic.
Do you know if it's possible to do what I'm trying to do with the arduino with something like this (https://www.davisinstruments.com/transmitters-and-sensors/#block1)?
Not in the sense you mean. The 6332 box does indeed convert the anemometer output into a digital format but then transmits it over proprietary wireless. So you need a suitable receiver and then to understand the data format. You could certainly use a receiver like Meteostick (or indeed a Davis Vue console plus logger or a Weatherlink Live unit). That could certainly work but would be substantial overkill. But obviously your call.
Or maybe this https://www.scaledinstruments.com/shop/ocean-controls/ocean-controls-ktl-250-12v-anemometer-modbus-interface-with-lcd/?
OC KTA250 would be another option, but the outputs aren't directly compatible with a Pi**. There is a Modbus HAT available I believe, though I've never used it, which would be one option for a digital interface. Or you could use the analogue outputs but then you hit the snag that the Pi doesn't have onboard A/D converters AFAIK. But again there are several A/D HATs on the market. But then if you're going to use an A/D HAT you could interface the 6410 direction direct to the HAT and use a Pi GPIO pin to connect to an interrupt for pulse counting. Not sure how reliable that is on a Pi, but assuming the Pi is dedicated and not doing much else then I guess it would be OK. But that's the reason that a microcontroller like an Arduino is often used for the primary sensor connection - there's no operating system to get in the way of timings and the MC can be dedicated to its task, while a downstream computer like a Pi can do the more complicated data manipulation etc.
All that said, and depending on the downstream application (you haven't said what you need to do with the data in detail) I'd personally be wondering whether a Raspberry Pi Pico maybe programmed in MicroPython or CircuitPython couldn't handle the whole job.
** Edit: Actually, I see that the latest KTA250 versions do seem to have a Modbus over USB option as well as Modbus over RS485 (but not Modbus over Ethernet AFAICS), so maybe a direct Pi connection via USB is possible. Presumably this is simply a serial Modbus connection delivered over USB via a virtual com port, but you'd need to work out how to speak Modbus across the interface (which might be trivial to do, but I've never tried).