Can you help with the difference in these past perfect tenses?

Example 1: 'Edison invented the light bulb. He had been working on it for years'. Example 2: 'Edison invented the light bulb. It had taken him years'.

In example 1, the past perfect continuous makes perfect sense, as working on an invention takes time and repeated effort. In example 2, the same argument could be made, yet we use the past perfect simple. Why?

Is it the 'dummy subject it'? Is it the verb 'to take years'?

Help please!

Is it the 'dummy subject it'?

No, it is a real subject. The It = the invention of the light bulb.

Is it the verb 'to take years'?

No. The verb is to take = to consume time. To use or spend (a specified amount of time) in an action, process, or activity; to require or allocate (a specified amount of time) (to do something). Also with direct and indirect object. Frequently with it as anticipatory subject and clause as complement.