6 months might be way too long for WiFi. A lot of factors come into place to achieve at least one month. Just to mention the most obvious is the frequency of data transfer.
So, max will be about some 10K per day.
I'm having trouble finding the same details about the MKRFOX1200 but for the transmitter "Low current consumption: 32.7mA during telegram transmit [...] Typical OFF mode current: 5nA." [1] The processor part is a SAMD21.
My guess is it's possible to get comparable idle/sleep power draw regardless of transmission method but WiFi will require more power to establish a connection and transmit the first byte.
[0] https://cdn-shop.adafruit.com/datasheets/ESP8266_Specificati...
[1] http://www.atmel.com/Images/Atmel-9372-Smart-RF-ATA8520_Data...
In most "connected" devices, you don't need to keep an established connection which will drain the battery fast.
This is why idle consumption is key, as it will often be the state of the solution 99.x% of the time
Simply turn the communication module on when you need it.
Then the difference between solutions consumption-wise will be on time needed to establish connection if any, time & power to send your data.