They attacked Kyiv with what they believed to be sufficient...

They attacked Kyiv with what they believed to be sufficient capabilities. Hostomel being a key target shows they intended to swiftly bring in additional forces by air, but they failed to hold Hostomel, and the whole operation thereafter imploded.

Attacking with much larger numbers to begin with would also have necessitated pre-war mobilisation, and massing much larger forces at the border, and would therefore have reduced their plausible deniability of imminent invasion and would therefore have met greater Ukrainian preparedness and stronger resistance from day 1.

And given their post-mobilisation 8 month slog to take little Bakhmut I think they still would have failed to take Kyiv even with greater numbers.