I don't have a problem with 'discord-only' RPs... if they're not being hosted on Feralheart. My personal preference is a mix of Discord and Feralheart. When you're in the middle of a long roleplay with someone, and they have to get off, moving it to Discord / being able to post the screenshots on Discord so you can return to the RP later is really great. Discord is also awesome for helping leaders of groups keep track of things, they can post their rules, have roster lists, etc.
Discord absolutely is advantageous because if you don't have the time to hop on Feralheart/aren't able to get on your computer for one reason or another, if you have the Discord mobile app, you can RP on the go.
I think that as long as some RPs are still conducted in game, there's nothing wrong with a mixed approach to roleplaying. I'm in multiple groups that both are in game and on Discord, and often times the Discord does get used more often, but not for lack of trying to RP in game. It's just easier to get on Discord and make a post than it is to get in game sometimes, and I think that's fair! I don't think that the use of Discord should be judged so harshly.
I actually require Discord for one of the RPs I run because I want to keep track of all of the members and have everyone be able to be social outside of just the game. So far, RPing on Discord has gone better than RPing in game. Every time we tried to RP in game, people had to go. Hopefully we can RP in game at some point, because I'd love to be able to see the beauty of Kibou Ridge while RPing since that's where I based the group. I wanted to make a simple, mapless wolf pack like the good old days, and yet we still have ended up using Discord more than in game so far. It happens.
TLDR, I'm a big fan of Discord. I'm able to get on much more frequently than I am able to get in game because I'm a busy person in real life. I can pop in to check on things/write a post with ease just by pulling out my phone. It's simple. I'm 100% for the idea of Mixed Discord/FH RP groups.