There are a few different points here. Firstly, there are plenty of unambiguous definitions of frontrunning that are accepted by the scientific community that this blatantly does fall under; see the Clark SoK we cite in our paper for this in the blockchain space, or the definition Wikipedia uses, which was from an economics article by Khan & Lu (https://papers.ssrn.com/sol3/papers.cfm?abstract_id=1140694): "trading by some parties in advance of large trades by other parties, in anticipation of profiting from the price movement that follows the large trade."
The second point here is even if you want to restrict the definition to require privileged information, privilege in p2p networks is not binary: there are some nodes that are better peered on the topology, have better mining equipment, etc. who can use these privileges to extract market rent, harming the security of a blockchain.
This is a complex and dense paper that took 8 people 18 months to produce, and I recommend you read it with an open mind, rather than having a gut reaction to whether we use your preferred definition of "frontrunning". I also recommend reading the primary source material directly, or at least my summary on Twitter - https://twitter.com/phildaian/status/1116155236433956865
Happy to answer any questions!