Yeah, sorry I keep harping on this, I just think that this is important enough everybody trying anything QoS is aware of it.
So DSCPs carry no inherent meaning and typically are only meaningful inside each individual diffserv domain, so we are not guaranteed to get useful/meaningful DSCPs from the internet/our ISP so resetting all packets' DSCP field to something harmless is IMHO the right thing to do (there are potential exceptions but these are rare and require your upstream to give you some guarantees).
Wheth ethe default should be CS1/LE or CS0 can be argued about until the cows come home. IMHO this is more a matter of personal preference and equally valid.
Yeah, cake is different, it will only reserve bandwith for the bulk class and only something like a 16/th of capacity, for other traffic each class will be scheduled preferentially for a certain amount of traffic and above that it will be scheduled round-robin (IIRC) with the lower classes. The upshot is that one should avoid packing greedy capacity seeking traffic into the higher classes (not a strict rule, but CS0 is IMHO the most suitable home for capacity seeking traffic in cake).
Yes of course, priority classes/tins will only affect scheduling if more than one contains packets.
EDIT: You wrote Wireshark, which I read but thought wireguard, so ignore my response. About wireshark/packetcaptures, yes that can be helpful, but keep in mind that changed DSCPs will only be visible on certain capturing places, e.g. if you capture on the WAN interface ingress packets with this script will all show the original internet/ISP DSCP values. So also look at the output of tc -s qdisc to see whether your test traffic increased the packet or byte counters in the expected cake tin.
Response to a question that was not asked....
Keep in mind that to cake all wireshark encrypted traffic will look like a single flow and hence it will not get as much tcapacity share as you might desire. @Lynx has cone up with an ingenious way of combining IFBs with policy based routing IIRC that sends wireguard traffic though the shaper unencrypted. If that is your problem, talk to him you will not regret it 
(I use neither elaborate QoS nor wireguard so can only argue on principles, @Lynx brings the goods as he actually has first hand experience).