It’s a little bit more complicated than that. On-hit items are few and far between for certain champs compared to crit items for a marksman, or AP for a mage. Irelia for instance on live, has BoRK and wits which work for her playstyle. The other options (nashors, rageblade, kraken), don’t really play because she doesn’t gain any kind of survivability from the stat profile of what is essentially an ADC item. Riot helped with this somewhat by giving her very high HP growth per level, but it still means that the shopkeeper doesn’t stock a robust assortment of options. After BoRK and wits that’s about it, and you then start just building generic fighter items or tank which is nowhere near the same amount of oomph for your autos/Q’s especially.

On-hit is just a weird stat for melee champs, and marksmen with their range make better use of them many times. This is not to say it’s a failure at all, but there is definitely some truth to BoRK being overly prescriptive in that you really don’t have many alternatives.

That said, terminus does look particularly strong to me in 14.1 if it stays the same as PBE