Whether it's too laborious for you or not I don't know, but what's certainly true is the fact that Gibbon's Decline and Fall is massively out of date. There's no denying that it's a classic work, and has been hugely influential over the centuries, but that doesn't change the fact that he's wrong a lot of the time. If you're interested in Roman History itself, rather than 18th century views on Roman History, there are many more recent works you would be better devoting your time to.

When I taught a course on Late Antiquity recently I used S. Mitchell, A History of the Later Roman Empire as the set text - it provides an excellent introduction to the period. I'd happily recommend other books too, if you're interested.