I have this 'Mech as a hand-made prototype from the RWR in my home/online campaign, with the final production line and variants not being established until they get to Terra. Makes sense to me that the RWR would have tried to make a staple, homegrown Heavy like they did with the Rampage and Phoenix. Especially since the doctrine of standardization was so widespread in the SLDF, which they tried to mimic.
Completing the conquest of Terra and THEN starting on a standardized Heavy (the most common 'Mech class in the Dragoon and Guard regiments) seems out-of-character, IMO. So... "whatever works on your table," etc.