Your car isn't 'effectively free', because you could sacrifice all £20k into the pension, paying no tax on it, and get the £12k in childcare subsidies because your income is <=£100k. The EV is costing you £7000 pa out of this.

It still might be desirable, but it isn't free.

If you're at that income level, your employer pension contribution is already likely high and you've likely been stacking it for a while anyway. At some point there is a diminishing return to how much you should put in your pension too; it's tax on exit after all. You only need 2-3 years of maxed out contributions in your late 20s/early 30s to set yourself up very well for the future.

If your income is that high the pension is likely something you have anyway