Copy UPDATEALL will be much quicker if you just want to do a one-way sync based on size & date, and don't need to see the interactive list of what will/won't be copied before the copying starts.
I agree the comparison stage can be slower than other tools, but Opus isn't a dedicated sync/diff tool. The sync tool in Opus is good for average sized jobs. (As in number of files to consider; size of files doesn't make much difference, unless doing a byte comparison.) For huge comparisons, dedicated tools will do better. Tools like Beyond Compare are great at what they do, and can be tightly integrated into Opus.
Of course, we might speed up Opus's sync tool comparisons in the future, but our focus is usually on areas where Opus can provide unique value. We could work for months on nothing but synching and still not offer more value than tools like Beyond Compare which have had people working on nothing but synching for years. (Similarly, Beyond Compare has some file management functionality built-in, but doesn't compete with Opus in that department. Horses for courses.)