Does it seem strange to you that Aegon’s conquest of Westeros didn’t bring about a similar appointment of Valyrians in high places of the nobility in the same way William’s conquest of England did for Normans? High Valyrian didn’t become the language of the court like French for the Normans in England. Outside of King’s Landing and the occasional lord in Harrenhal the Valyrian presence seemed very tiny.

I don’t think it’s strange as much as a deliberate choice by GRRM. 

After Hastings, William’s control of England required him to maintain the loyalty of the army he had gathered from across Northern France (mostly from Normandy, but there were also quite a few from Brittany and Flanders, Bolougne) by redistributing English land to his followers. He could also use English land as a way to entice new reinforcements to cross the Channel.

Aegon had a different situation: he had a very small number of followers to be rewarded – “accounts differ on how many swords set sail from Dragonstone with Aegon and his sisters. Some say three thousand; others number them only in the hundreds.” (WOIAF) – and more importantly, it was really his and his sisters dragons that won him Westeros. When you look at the Conquest, whether it’s the capture of the Vale by Visenya after Daemon Velaryon’s fleet was defeated in the waters off of Gulttown, or Aegon burning Harrenhal, or Rhaenys’ dragon blocking Argilac’s final charge at the Last Storm, or the three dragons together at the Field of Fire while most of Aegon’s infantry broke on the field, it’s always the dragons who are the deciding factors and who are often saving the day when his conventional forces fail.

So Aegon had less of a pressing need to reward the Valyrians who he brought from Dragonstone and Blackwater Bay, and more of a need to pacify the pre-existing power structure through maintaining the social contract.