plastics and carbon fiber are made with hydrocarbons generally. Aluminum might actually be worse, since aluminum requires very high amounts of energy to produce.
Solar energy used to produce aluminum has zero marginal cost. So, unless you assume use of fossil fuels to produce the power used to refine the aluminum, this is nonsense.
Hydrocarbons are not a problem per se. It's burning the hydrocarbons, specifically the carbon part, which has the detrimental effect on climate.
Plastics and carbon fiber effectively keep the carbon from becoming CO₂.
Aluminum takes a lot of energy, but, unlike steel, the process does not release any CO₂, and is fully electric. It can be powered by hydro (and often is), nuclear, or solar energy directly.That's the point.