I have done endurance cross country races on a gravel bike because why not I guess and while the experiment was intriguing it beats you to all hell afterwards. Having to be insanely careful with line choice gets old after 10 mins. Also done XC circuit races as well and those are definitely fun on the gravel bike as circuit races are nothing more than "off-road" gravel races. Will I get rid of my XC bike for a gravel bike? No way in hell. Underbiking can be fun but it's not a long term thing. I will say though that gravel bike is probably the most versatile of the bunch because at least where I live I can race 3 displines with it.
road
gravel
cross country circuit
Although I will say cutting out road riding out of my life has been for the better. No longer have to worry about being run over by a dumbass on the side of the road. My N+1 has just become versatile because of it too.
Gravel bike
120/120 MTB
160/160 MTB