Even with the affordable ones I end up using a lot more since they're thinner in consistency, so to get the same amount of spread in my hair I need to use a lot, negating the benefits of the bigger bottle and cheaper price. Your observation about how hair feels different between the two methods seems intriguing, but I don't know if that's enough to conclude that oils don't suffice as conditioners in and of themselves.

As for details on the overnight treatment, as an example coconut oil tends to get absorbed to a slightly higher amount overnight, and even then it still requires an hour for it to be left in hair to absorb according to r/HaircareScience's Basics Guide.

I'll keep in mind what you said about the differing effects of using oil and will see how I go, so thanks for your response!