Sostratus
Deity
It may be counter intuitive but adding a unit between knights and tanks, as there appears to be in the shot of the tech tree during the hungary stream, only increases the value of knights.maybe along with adding a unit in between knights and tanks, the former will be reduced a bit in power.
Status Quo: Knights are very effective units well into the renaissance (because they are way faster than infantry and still hit decently hard.)
Adding a new unit: knights can do everything the same as before, but you can also upgrade them to make them better
Since nothing about the status quo has been invalidated, and an option for more power has been added (which, regardless of specifics, player would only take if it was worth it) means knights won't be any weaker than before.
No, the only way to make knights less dominant is to add more competitive options to their contemporaries.
This would be, just looking at what units are available in each line when knights take the field:
swords
xbows
pikes
horsemen
When you look at this list, you probably notice all those units suck compared to knights. And they kinda do. Basic Swords in the Medieval just cannot really stand in as anything but pike slayers (promoted ones can kinda take crossbows) and crossbows just don't have the punch to stop knights without a meat-shield. Which would be the pikes, which are not effective. If they do not balance coursers properly, then we will end up with horse-> courser instead of chariot->knight because its easier to use horses than chariots and coursers may well be just as good as knights - the Black Army as shown would be even better!
The more you fill in a unit line, the closer its power curve gets to the "contemporary unit" curve and the less 'loss' there is from not being strong enough. Think of a step pyramid (unit gaps) vs a smooth pyramid (no gaps) - the step better approximates the smooth the more steps there are.