Simply, the avenger is better damage.
Which is questionable to be worth all the extra effort and requirements. But definetly saw it's use already, and will do in future.
However, while it's not hard to pick up something from army of small guns (just to be honest X70 is the least remarkable weapon, as the most fallout players did really never touched it, but still better than implementing caseless amunition)
What would be the counter for those from other weapon types. Yes, gatling laser is going to oneshot anything that will wear worse armor than MA, and above that just do average damage, but still can be sort of a fun - however what's up with melee weapons - they've already gotten ripper or upgraded cattle prods or just megapowerfists for quite some time, yet nobody cares to bring more than spiked knuckles.
And afterall, isn't it just contradiction to promise of making low-tech stuff more useful, when there are weapons of this kind?