The Bible's main point is God's plan for salvation, which is inherently "optimistic." Referring to temporal eschatological matters is necessarily less significant than that plan for eternal salvation. To coin the phrase "Biblically Optimistic" conjures up the prospect by inference of its converse, which suggests that the salvation plan described therein must be flawed. That would be a gross fundamental misunderstanding of the Bible.
If what you mean is eschatological rather than soteriological, why not make it plain?
"Biblically optimistic" has to do with the measurable positive effect the gospel will have in the world over the course of history.