Even under definition 2, it still means 'reduce'. So if the salary was 'reduced', the second offer was less than the first one. It may have 'decimated the attractiveness' of the first salary, sure.
Please tell me you are trolling:
Drastically reduce the strength or effectiveness of (something): "plant viruses that can decimate yields".
decimated Intel's offer.
Drastically reduce the effectiveness of Intel's offer.
It fits exactly. Not only that, but you could also say:
Destroyed Intel's offer. (Def 1)
Decimate is the right word choice and it conveyed the intensity of how badly Finance Co. beat Intel's offer. Your definition of decimate may be used by heavy quants but it doesn't fit everyday usage.
decimated:
past participle, past tense of dec·i·mate (Verb) Verb
1) Kill, destroy, or remove a large percentage of.
2) Drastically reduce the strength or effectiveness of (something): "plant viruses that can decimate yields".