So, I'm gonna say this same statement as I have in other threads. Why this urge to "jump to another brand"? If you like your Canon setup for certain things, but it's lacking in others, why not buy another brand for that purpose? How many people have 2+ Canon cameras for different use cases? Why can't you have multiple brands? I have pre-ordered a Fujifilm X100VI because Canon right now doesn't make anything like that. I'm not switching to Fujifilm, I'm keeping my Canon gear for what it does good, and I'm buying a Fujifilm for what (I hope) it does good.
Maybe he's doing something like ceremonies, weddings, events, etc, and needs cameras with common batteries, lenses, flash triggers, etc.
Example, I want the Tamron 35-150 SO BAD; I could hold onto my R6, and ditch my backup body (Eos R) to buy a A7III to use the Tamron with, while I'll use my bright primes (40 Art and 105 Art) alternatively on the R6.
I buy the A7III with the R money (they cost the same used), but to buy the 35-150, I need to sell the 24-70 and 70-200. Switch must be zero charge.
Now, if the R6 dies in the field, I can use all the lenses (included the Sigma DSLR primes via MC-11 adapter) on the Sony; but if the Sony dies? Then I find myself with two beautiful primes on the R6, but certainly not that flexible, and the 35-150 zoom it's useless (and I already sold my two Canon zooms to buy the Tamron), and nothing wider then 40mm, so not an ideal situation (even if you certainly can do a wedding just with a 40 and a 105 if needed).
So, it's not so uncommon to think "well, the moment I buy a Sony alternative, then I'll just buy two of them and ditch both R and R6 altogether"; I thought that already, but haven't pulled the trigger, yet. But maybe he has different needs, and urges, then me.
Yes, many people have different brands to do different things; but if you need to do just one thing, or different things but with need of backup, then you (usually) just want one single brand, not two or three.