With EIGRP the bandwidth reduction in the path due to a failed link in a port channel won't affect the metric but, with the idea of converting to OSPF I can see a case for going to ECMP; although ...

EIGRP does have summarization capabilities, but again it doesn’t make you think too much about your topology, which again can get you into trouble as the topology grows.

3) Configure EIGRP such that R1 has exactly one EIGRP route for subnet 172.16.1.0/25, which uses R1’s S0/0/0 (or equivalent in your pod) as the outgoing interface.

With 2 blobs separated by 172.16/12 that works fine, if you add a 3rd it'll blow up. Basically I think they picked a poor topology to try and demonstrate an understanding of autosummarization.

Equal-cost multi-path allows a router to insert more than one path to a destination in the routing table to enable load balancing. Here's how ECMP works and how to configure it in OSPF.