This is strictly a user preference - use whichever of the methods meets your needs. Most users who end up using Pi-Hole DHCP do so because (1) their ISP router will not let them assign DNS to Pi-Hole, or (2) their router will not show individual client IPs.
I run several pairs of Pi-Holes, and it is easiest for me to assign static IP's for all the network clients in one place - my router. I see individual client IP's in Pi-Hole, and I have the static IPs mapped to client names in /etc/hosts on the Pi.
If your current configuration provides what you need, stick with it. I do notice in your debug log that the queries shown all appear to originate from the router, when in fact they likely originated at one of the network clients.
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Rather than whitelist what others have whitelisted, take a look at what is being blocked and selectively whitelist as necessary. These tools can be quite helpful: