Keep in mind that OA eligibility is normally at least 5 nights from one camp of 5 or more nights plus at least 10 nights from camps of 4 or fewer nights, all within the two years preceding the OA election.
Currently, there are modified requirements in place for the 2021 program year that permit counting effectively all BSA camping nights within the preceding two years, due to the restrictions that have been in place limiting group activities (like unit camping) in many parts of the country. More details on the temporary requirements are here:
OA Temporary Camping Requirement Changes | Order of the Arrow, Boy Scouts of America
I recommend reading them carefully and thoroughly, as there have been multiple incremental temporary changes over the last couple of years due to COVID, some of which supercede one another.
On a separate note, I would offer my personal view that no trip is ever “for nothing”, Philmont and other High Adventure trips least of all. It may or may not count towards advancement, but advancement is not the reason to go on outings, nor is it the purpose of Scouting.
High Adventure, in my opinion, is the opportunity to put into practice all of the lessons we learn as scouts: teamwork, planning, performance under pressure, leadership, technical skills…These are the bread and butter of what a High Adventure trip requires for fun and successful execution.
I think there are two different things going on that compete in the requirements. One is the desire to set a “reasonable” number of camping nights for Camping MB. The other is the desire to avoid most or all of those nights coming from summer camp experiences. As a result, “long term” camps get lumped together, whether they are long-term “stationary” camps or long-term “mobile” camps. Could it be done differently? Most likely, but the only way to lobby for that change is with the Advancement Team.