There are many ways to determine field strength. It is an extremely difficult job given that AMTA tries to keep regionals, well, regional, and there are many factors to balance. I respect the relevant committee members very much.
I thought this was one of many possible interesting metrics to look at: number of teams in last year's National Championship Tournament Top 10 and Honorable Mention. I fully embrace that the choice of this metric is influenced by my own biases.
Three Top 10 Finishes
Jamaica (Columbia A, NYU A, Penn A)
Two Top 10 Finishes
New Haven (George Washington A, Yale A)
Los Angeles (Irvine A, UCLA B)
Orlando (Furman A, Furman B)
Spokane (Stanford A, Cal A)
One Top 10 Finish; One Honorable Mention
Chapel Hill (Duke A; Washington and Lee A)
Louisville (EKU A; Tennessee A)
Cincinnati (Miami B; Miami A)
One Top 10 Finish
Fresno (UCLA A)
Syracuse (Cornell A)
Baltimore (Richmond A)
Topeka (Iowa A)
Princeton (Georgetown A)
South Bend (Northwood A)
Zero Top 10 Finishes; Three Honorable Mentions
Columbia (Wash U A, Rhodes A, Rhodes B)
Zero Top 10 Finishes; Two Honorable Mentions
Milwaukee (Northwestern B, Northwestern A)
Zero Top 10 Finishes; One Honorable Mention
Providence (Boston University A)
Joliet (Michigan B)
Zero Top 10 Finishes; Zero Honorable Mentions
Davenport
Houston
Superior
Worcester
Birmingham