Tbh the only really extremely dark Gundam series are IBO, Thunderbolt and maybe Narrative, and Thunderbolt's the only one I'd call outright torture porn. Sure Victory was dark but it had a really hopeful ending, most of Uso's friends survived I'd hardly call it a bloodbath ending. If G-Witch ends up going into super grim nihilism by the end I'd chalk that to the writers misunderstanding the series rather than some inevitability about the series itself.