At least in my case.
This week a close friend told me that he is replacing his Nikon D800 with a Z6ii. This got me thinking again: just how much weight could I save by going mirrorless? My impression is that the weight savings people notice is because of format, not mirrorless per se, although it clearly depends on the brand and model. I decided to calculate this for my own equipment.
My main body is a Canon 5D mark IV, and my most common walk-around lens is the 24-105 f/4 L II. That combination is 1595 g, or roughly 3.5 pounds. At this age, I would love to have something that weighs less. The replacement body is the R5, and Canon has an R-mount replacement for the 24-105. That pair weighs only 10% less, 1438g. If I do down a notch to the R6 (more advanced in some respects because it's newer, but with much lower resolution, less weather sealing, and no top LCD), the weight savings is a bit more because the chassis has more plastic, but still only 13%. Specifically, the savings is 157 g with the R5 and 215 g with the R6.
But that's not all of it. Unless I replace all of my lenses--and most of mine are excellent and in mint condition--I need to add an adapter. The simplest one weighs 110 g.
Then I went a step farther: what if I splurged and replaced my EF 70-200 f/4, my second-most used lens, with the RF replacement? That would save only an 85 g. It would also not require the 110g adapter, but I would have to carry that anyway if I carry any other lenses.
Bottom line for me is that if weight really becomes a problem, I'll need to consider a smaller-format camera. However, even that would only help a lot if I switched brands because it now seems like the new Canon APS-C model, if it actually is coming, is probably R-mount.
And, of course, I lost one excuse to upgrade.