TDO shows how well your pokémon will perform in Great, Ultra, and Master League among the 4096 possible IV combinations by quantifying the pokémon's strength in PvP.
In Gym, Raid, and Master League, one of the largest determining factor for the strength is Attack IV.
However, in Great/Ultra League, the high Attack IV may make your pokémon weaker than the same species with lower Attack IV.
Since CP gives weight to Attack IV, the more the pokémon has the high Attack value, the more its degree of the CP increase per powering up goes up.
Hence, when you power up your pokémon until it hits to the limit (1500cp or 2500cp), the overall strength of the pokémon with higher Attack IV will end up with falling below that of the one with lower Attack IV.
In this sense, it can be said that what matters in PvP (especially in Great League and Ultra League) is not how high the total of IVs is but the IV combination, how the IVs consist of.
In an effort to examine which IV combinations enable a pokémon both to reach nearly 1500/2500cp and to perform well in each league, we employed the follwing formula:
TDO = (((ATK+ATKIV) * CPM) * ((DEF+DEFIV) * CPM) * floor((HP+HPIV) * CPM)) / 1000
* /1000 is added for minimizing the number of the results.
* Damage formula calculates the digits after the decimal point which Attack and Defense have but it cuts off after the decimal point of Stamina to the nearest whole number.
This formula, as you can see, considers all the components of IVs (Attack, Defense, and Stamina) equivalently so as to extract the best IVs for each league from 4096 combinations (16 * 16 * 16).
On the basis of this formula, a pokémon with higher Stamina/Defence and lower Attack tends to have the higher TDO (you can confirm this fact by checking PokeBattler's examination
and u/MannishBoyX's post
*TDO in Poke Rookie aims to compare, rate, and rank the IV combinations for one species per league. This TDO doesn't take into account DPS (moveset) and the comparison with the other species.