Therefore, the question of whether it's a "prime killer" is moot. It's a hypothetical lens.
However, we *can* discuss the general idea of a hypothetical super-high-quality, fast zoom lens and whether it could potentially replace prime lenses for some photographers:
Could a theoretical 100-300mm f/2.8 zoom lens be a "prime killer" if it existed and was exceptionally well-made?
Maybe, *for some photographers*. Here's a breakdown of why and why not:
Arguments FOR it being a "prime killer" (or at least reducing prime use):
* Versatility: The biggest advantage is the zoom range. Having 100mm, 135mm, 200mm, and 300mm all in one lens is incredibly flexible. A photographer could quickly adapt to changing situations without swapping lenses.
* Fast Aperture: f/2.8 is a very wide aperture, comparable to many fast prime lenses. It would allow for shallow depth of field and excellent low-light performance.
* Image Quality (Hypothetically): If Canon designed this lens to the absolute peak of optical performance, it *could* theoretically approach the image quality of some prime lenses. Modern lens design and manufacturing techniques are constantly improving.
* Convenience: Carrying one lens instead of multiple is a significant advantage, especially for travel or fast-paced shooting environments.
Arguments AGAINST it being a "prime killer":
* Size and Weight: A real-world 100-300mm f/2.8 would be enormous and incredibly heavy. This alone would be a deal-breaker for many photographers. The bulk would make it difficult to handle and transport.
* Cost: Even if technically feasible, such a lens would likely cost a small fortune, putting it out of reach for most photographers.
* Image Quality (Realistically): While possible to get close, even the best zoom lenses typically make some compromises compared to prime lenses that are specifically designed for a single focal length. You *might* see slightly less sharpness, more distortion at certain focal lengths, or less perfect rendering of out-of-focus areas (bokeh). For pixel-peepers, this could be a deal-breaker.
* Specialized Primes: Certain prime lenses offer characteristics that a zoom simply can't replicate. For example, macro primes are specifically designed for close-up work and offer unique features like 1:1 magnification. Similarly, tilt-shift lenses offer perspective control that no zoom can match.
* "Feel" and User Experience: Many photographers prefer the tactile experience of using a prime lens. The simplicity of a fixed focal length can encourage more deliberate composition and creativity.
Conclusion:
A hypothetical, exceptionally well-made Canon 100-300mm f/2.8 *could* reduce the need for some prime lenses for *some* photographers. Those who prioritize versatility and convenience above all else might find it a worthwhile (albeit extremely expensive) alternative.
However, it's unlikely to completely replace primes. The size, weight, cost, and potential (albeit small) compromises in image quality would still make dedicated prime lenses a preferable choice for many photographers, especially those who demand the absolute best optical performance or require specialized features. And of course, there is something to be said for the enjoyment of using a prime lens.
The key takeaway is that lens choice is always a matter of personal preference and depends on individual shooting needs and priorities.