[ThrowawayR2]

Personally, I would recommend taking the C++ role to broaden your abilities. Being able to do both C++ and webdev means that you have more options later in your career when you want to switch jobs (very valuable during an economic downturn) and are, depending on the employer, potentially more valuable to them for being able to do both types of work when necessary.

You can always fall back to being a web developer later if you decide that isn't for you since web dev jobs are both extremely common with demand still growing and often have a lower bar to entry, as demonstrated by the success of bootcamp graduates and the large contingent of HNers trumpeting that a CS education hasn't been useful to them.