The phrase "altogether optimistic" is correct and usable in written English.
It can be used to express a complete or total sense of optimism about a situation or outcome.
Example: "Despite the challenges we faced, I remain altogether optimistic about the future of our project."
Alternatives: "completely optimistic" or "entirely optimistic".
"We are not altogether optimistic about this visit.
But Van Duyn's version of the world is not altogether optimistic.
Sagan was not altogether optimistic about the future of his own species: the threat of nuclear annihilation is a motif of the original "Cosmos".
The tone suggested the German and French leaders are not altogether optimistic of finding an agreement among the wider 27 nations of the EU, but if those negotiations break down, said Mr Sarkozy, then we will have a treaty for the 17 members of the eurozone.
His thoughts on the present state of affairs weren't altogether optimistic.
On stage in Stockholm tonight, the song becomes something altogether more optimistic: a statement of defiance.
But it was with Tony Blair that the argument for moving from industry to services shifted from one of dire necessity to being an altogether more optimistic vision about Britain's place in the world.
In 1981, it was followed by the altogether less optimistic No Gods and Precious Few Heroes: Scotland since 1914, the eighth volume of the New History of Scotland (Edward Arnold, later Edinburgh University Press, latest edition 1999; new edition in preparation).
In some ways the movie resembles Easy Rider, a picture made when Che's posthumous reputation was at its height, but it's altogether more cheerful, optimistic, benevolent, and Ernesto and Alberto are far more likeable and idealistic than the fashionable heroes of Dennis Hopper's movie.
When feedback signals declining performance, listeners eventually stop learning altogether, presumably because the optimistic bias does not offset the demotivating effect of feedback.
Not so long ago, the idea of Mr Putin presiding over a gathering of free-market democracies might have seemed optimistic, but not altogether implausible.
