I think your lens example is a bit flawed. Yes putting steel wool in your kit because you plan on using it and a battery is stretching; kind of like carrying a bow drill set up. You should practice building a bowdrill set so that you can make one in the field. Not carry one around unless that is the type of "outing" you are planning on.
But the lense is something that cannot get wet or run out of fuel.
The community at large agrees on the need to have multiple ways to make fire; usually 3. The lens is a no-weight, no-bulk way of starting a fire. Why would you not make it one of your 3 or 4 ways? Even if you never need it it takes no space.
Having such a small back-up seems to be logical.