Yes. Since FSK is on 868.8MHz and close only to RX2 window frequency and it’s 10 times faster than SF7BW125 and in different modulation it’s like having extra 10 channels. In contrast SF7BW250 is not attractive to the network since it’s on the middle of mandatory - join - frequencies. So twice the speed but annoying to the three mandatory channels.
FSK seems fine.
You can receive downlinks with FSK? I fail with SF7BW250.