First of all time investment versus reward differs between players and what SE has in mind. Secondly, the stats on the relic isn't the single reward the weapon provides which many seem to overlook (yet the fact that it is unique and different is why so many want it and complain about it being hard to get because of its heavy time investment requirement). If we really want to talk about time investment equaling reward, then I must say relic by far beats out all the beast tribes except ixal in terms of time required and the rewards you get for it. Does that mean beast tribes are in a serious need of buffs or nerfs? Not at all. Because the rewards are what SE deemed the time investment to be equal to. That exact same logic applies to the relic. And for reference, if you are decently invested into it, it takes less than 30 days to get a relic to i125 from scratch.
The same can't be said for beast tribes.
Edit: And yes I know the ACTUAL time investment between the two are grossly different but you still can't max out a beast tribe faster than 28.5 days where as how fast you do relic is completely up to yourself.
