Thomas Aquinas on Diversity

Being asked where to find Thomas' teaching on Diversity (a quote that can be found in various contemporary writings, but either not referenced or falsely referenced), we read the following in his commentary on the Sentences d. XLIV q. 2 resp. writes as follows: '

et ideo melius est universum in quo sunt angeli et aliae res, quam ubi essent angeli tantum, quia perfectio universi attenditur essentialiter secundum diversitatem naturarum, quibus implentur diversi gradus bonitatis, et non secundum multiplicationem individuorum in una natura.