I've always hated this in reviews. No, you're not "showing the real difference by eliminating bottlenecks" - you're instead changing the entire performance landscape you operate under and then getting spurious results. If you had unlimited time it'd be nice to see a good variety of platforms and graphics cards and so on, but the real-world performance is going to be on a budget-appropriate motherboard and with matching GPU. If that results in the CPUs being tied then, well, the CPUs were tied. It also gives people a lot better ability to see where to spend money on a system - what would make a difference vs what only looks like it makes a difference cause we massaged the scenario to make an artificial load on one component.
I also realise tech reviews are primarily about entertainment and engagement, neither of which is well served by finding no appreciable differences.