Build estimate
Core i5-12400F and RTX 4070 bottleneck estimate
The RTX 4070 can outrun the Core i5-12400F in some 1080p high-refresh games. At 1440p, the combination becomes more balanced because the graphics card has more rendering work to do.
1080p
Expect CPU limits in games that push very high frame rates or rely heavily on simulation. If GPU usage is low while FPS is stuck below your target, the processor is likely the limiter.
1440p
The pair is more reasonable at 1440p. The RTX 4070 is strong for this resolution, and the i5-12400F remains usable unless the game is unusually CPU-heavy.
Upgrade advice
Choose a CPU upgrade for competitive 1080p/high-refresh goals. Choose a GPU-focused settings path for 1440p visual quality, where the RTX 4070 is already the major performance asset.