Even if the average application data rates is less than the capabilities of each and every link for packet switch, we still need congestion control as we are only given AVERAGE but that doesn’t guarantee the peak. Because of the bursty nature of the traffic, we still need congestion control, unless the peak is less than the capabilities of each and every link.
Nodal processing delay is always negligible.
Sometimes the up link and down link may take different routes.
In traceroute program, by default, a probe landed on the same hop doesn’t necessarily take the same path as other probes that also arrive on that hop.
Traceroute is essentially a sampling tool. It doesn't force a path; it just reports back on whatever path the network's current routing logic decided to send those specific packets. If the network is splitting traffic, traceroute simply reveals that split by showing you multiple "Entry 7" routers.