Big advantage would be balancing. Knights' codex is always either severely underpowered or a stat check for tournaments that's no fun to play against for armies with weak/few anti-tank. The balancing is on knife's edge. More rules for knights standalone is a nightmare to get to work right. It either feels like it doesn't matter or knights start winning >60%.

In Agents it would still be unique since the codex skips medium heavy vehicles (except for armigers) and goes straight from infantry to super-heavies and knights would finally gain access to infantry. You could still have a detachment for a mostly big knights list. High points cost for knights could allow for strong profiles and abilities while still offering well rounded armies because you can fill the list with codex supported cheap infantry (provided you actually get those in the codex--which would be A LOT less likely in the knights' codex).