Dear Matteo,46T is perfectly fine, because associated with an 11T sprocket it gives you about 50 km\h at 100 RPM.
At the moment, for example, I am riding a 50/34 crankset with a 14/34 cassette since I live in the Alps and most of my rides, considering 50 km segments, have an average elevation gain of 1000 m.
I am lucky enough to live near by many famous climbs of the Giro d'Italia and Tour de France, as well as famous valleys dedicated to MTB (for example Valle Maira, where I always find many tourists/bikers from Germany). In these places the problem is not going down, rather, it is having the appropriate gearing for going up decently.
46/30 crankset paired with 11/30 or 11/32 cassette is perfect. The only downside of using the Grizl with road tires could be aerodynamics, because the frame and fork are wider and bigger to ensure compatibility with 50 mm tires. This impacts negatively on the aerodynamics of the bike, and it could be a noticeable factor for my long summer rides on the alpine climbs of the Giro and Tour....very long rides (150-200-250 km) where there are many difficult climbs but also long valleys where you might have to ride for 1 or 2 hours between 25 and 35 km\h. In that case, aerodynamics becomes important to save energy for the next climb.
riding road race bikes, cyclocrossers and MTBs since decades I do not see an issue using the grizl on those rides you described if you choose the right wheel set. I am riding on road with my cyclocross bikes (resembling the grizl chracteristics) in the Odenwald and I did not notice a positive effect of using deep section (60 mm) wheels on >2,000 ascent m rides compared to a lightweight (non aero, 21 mm) wheelset. I still believe in the advantage of light wheelsets on time consuming uphills compared to the aero advantage of a deep section wheel (aero frame) on such rides.
Therefore you might consider choosing a cyclocross frame (eg inflite cf slx) instead of the grizl. For me 40 mm tires are enough for on/off road rides. On any ride with noticable sections of DH gravel (expecting roots, stones) I would definitely choose a hardtail at least. Even with 50 mm tires a rigid bike is no fun going DH on gravel / trails becaus the risk of snake bites is high.
Erdnah