It's really not. It's just getting started. The worst predictions, of 4-6 degrees of warming, are more or less off the table. Current trajectory is ~3 degrees of warming which... is civilisationally devastating admittedly, but we have pathways to reduce that. Even the 1.5c target isn't over yet.
There is a broad range of potential future climates, and this generation decides which one we end up with. It's not over by a long shot.
It's not a matter of optimism, it's a matter of not repeating our parents' mistakes. Whatever the inevitability of warming, we should fight for every 0.1°C, because there's a big difference for our kids if the average is 2 or 5 or 6 degrees higher.
You can be as pessimistic as you feel the need to, as long as that doesn't stop you from acting.
I'm glad you're optimistic but warming has a roughly 40 year delayed effect and we're already seeing changes. Even if by some magic we halted all emissions, and I mean ALL, we'd still be warming into the 2060s.
The only way to make the 1.5c target would be a massive investment in carbon capture and huge reduction in carbon emissions.
I just don't see it happening. I don't see the world even trying until it's too late.
Some of this delayed effect has been debated, but we ought to consider the cascading effects as well.
It's true that there is huge inertia (transfer of heat and carbon from surface to deep ocean, and melting ice), also 'cascading events', but after decades of research these are mostly baked into the model projections. Below 1.5C seems very hard now, but well below 2C is certainly doable. What's not so baked in, is society inertia - 'not even trying until ...', that we have to change.