Roman use of the Contus

[Frank]

I don't think Romans introduced contus till reign of Hadrian & even after that the javelin was primary cavary weapon for Roman horsemen for a while?

Afaik heavy cavalry / cataphracts never became the main cavalry force of the romans.

Even in the parthian or sarmatian armies, cataphracts were not the strongest part. Historians guess about 10% cataphracts for the parthian cavalry. Perhaps a bit more for the sarmatians. The rest is light cavalry primarily mounted archers. And finally, not every mounted lancer with a contus is a cataphract or shock cavalry.