When did the Roman Empire fall (your thoughts)?

[Theodosius the Great]

I finally finished Greg Woolf's Rome: An Empire's Story, which suggests the Empire fell circa the early eighth century.

When the east lost control of its western (re)conquests?

Interesting view. It sounds like it ties in with how other authors date the beginning of the Middle Ages to the coming of Islam (i.e. the Arab conquests). It sounds like Woolf is pointing out the good reasons behind this but goes further in refuting the claims of the emperors in Constantinople. If so, I can't agree with him. Even after the loss of Egypt, Syria, Africa, Italy, and Spain the empire was able to project power disproportionate to its size against the behemoth Caliphate.

They did their best and by 268-75 saved the Empire.

Yes they did. I was differing on their motives.

Sure but the surprising thing is, barbarian groups occupied just about every nook and cranny in the West but in the East didn't go beyond the balkans into Asia Minor, Syria, Egypt etc.

Yes, due mainly to the defenses of Constantinople which often saw these groups pay a visit.

But they were catholic churches which arians weren't so enamored of.

Such distinctions didn't faze the new overlords. They appropriated what they wanted.
Besides, the Franks were never Arians. Clovis converted to Catholicism from paganism. The subsequent history of the Franks show this didn't dull their edge one bit, IMO.

~Theo