Saul, in his jealousy, misses out on crucial features of Hebrew poetry.
In their victory songs, the Israelite women celebrate that Saul has killed his thousands (alefav) and David has killed his multitudes (ribbotav). Saul was greatly incensed at this, seeing his inferiority to David in the lyrics. Certainly, it is true that a ribbah can be greater that an alef (Deuteronomy 32:30, Judges 20:10), but it could also simply be an indeterminate large number, not specifically 10 thousand, as frequently translated. In either case, the key characteristics of Hebrew poetry, such as the song that Saul objects to, is parallelism, and here as essentially rhymed ideas. “Saul and David both killed lots of Philistines” is the point of the song, not to specify some sort of morbid kill-count. Saul is looking to become jealous. The Hebrew words here are not as specific on David’s number as most English translations would suggest. Another, less jealous, king could have simply interpreted the lyric inoffensively.