The other problem with ALL of the NEW mirrorless cameras is the lenses.
This is a problem that ALL manufacturers have. They cannot release 20+ new lenses all at once, it has to be done over several/many years. Nikon's Z system lens roadmap is over 5 years. I heard it took Sony 5+ years to flesh out their lens line-up.
Do they have the lens that you want, NOW. Or do you have to wait several years for that lens to be released? And can you wait that long?
You are in a different position than an existing dSLR photographer who has lenses. In the case of dSLR photographers, most of the manufactuers make an adapter to adapt their current lenses to the new mirrorless camera.
In your case, you would have to buy a dSLR lens, not a native mirrorless lens, and use the adapter.
Existing systems such as Sony, micro 4/3 (Olympus and Panasonic), are systems where you have an existing lens landscape to pick from.
Caution, the Sigma lenses have FIXED mounts. IOW, you cannot swap a mount adapter to move from one system to another (ie. Canon to Nikon).
While they do have adapters for dSLR lenses to mirrorless cameras, some combinations do NOT work well, such as Nikon-F to micro 4/3.