tbh - just stick with what you think is the best explanation.
And i and James Cameron think it's the Alien queen.
Ridley Scott thinks it's the 'morphs a human into an egg thing'
And since Ridley scott made Alien (a masterpiece), Prometheus and Alien: Covenent (total bullcrap) i think Ridley scott has nothing to say in this matter and we stick to the Alien Queen lorewise
That's also the reason i ditch all bloodburster and Protoalien crap from my Alien RPG ;D
I think it can be both. If there's no queen around the question does become "how do we get a new queen and/or eggs?" The egg morphing thing is a nice solution to that quandary.
Maybe the answer just is: you don't.
Maybe killing the queen and destroying the eggs means the infection is stopped, and it's "just" a matter of mopping up the remaining xenomorphs. I mean, from a story telling point of view there can always be one more egg hidden away, with a queen facehugger in it.
The interesting thing is that when you look at what we now know about how the Alien embryo is implanted and the black goo itself egg morphing seems more plausible than it did before the prequels. Ironically, we've misunderstood egg morphing for years. I have at least. According to Ridley Scott Brett wasn't literally morphing into an egg. He was just a food source for an egg that was slowly growing.
If you're not aware of what I refer to with the embryo implantation, I think most people picture it as the facehugger literally putting an egg or embryo down the victims throat. But in actuality, what it does is put some kind of liquid containing a retrovirus in the victim. This virus then breaks down the surrounding tissue and builds the embryo out of the victims own body. This is a big part of why the Xenomorphs take on the characteristics of the hosts. Ash wasn't too far off when he called the one on the Nostromo "Kane's son."
So, yeah, knowing all this, I think egg morphing make sense if a Xeno is in a situation with no hive and queen. It allows a single xeno to slowly build its own hive. It also makes a single xeno a threat to an entire colony or world.