Many ingredients play many different roles depending how you use them, they have major and minor properties. Cationic surfactants are weak cleansers because they emulsify (mix oil with water) but you have to use massage and rinsing to make them do that. If you just smooth onto hair, soak and rinse they will stick to the hair and reduce friction (condition). That is really useful in formulation, you can 'ask' one ingredient to perform several tasks.
It is like you eat oily fish that is a good source of essential fatty acids, protein, vitamin D and various other vitamins and minerals. Or you can make an egg into various things, you could eat raw in a shake (ugh!), or have hard boiled or soft fried or scrambled. A balanced diet is eating a certain number of portions from different food groups so that you get all the nutrients; a balanced haircare routine is similar. They key is putting products and ingredients into the right 'food groups' so you get a balance which NC can help you with if you post up ingredients lists.
Because most ingredients that condition hair do that by adhering to the surface in theory many of them could build up if you don't cleanse your hair properly
. They are not all likely to build up tho, the ones that are likely to build up include many silicones (not all), some polyquats (not all), butters, mineral oil/ petrolatum, waxes including cetyl esters.
Most natural oils will not build up, nor will the cationic surfactants you mention unless you are not cleansing properly. Some conditioning agents can sometimes cause scummy build up if mixed with shampoo, the solution is not to do that, rinse your leave in conditioner away carefully before applying shampoo.
Some of the problems we have here on NC are down to people not cleansing their hair properly and/ or overusing ingredients that are likely to build up. Cleansers are there to cleanse without stripping, not condition or 'moisturise' they can't effectively do both at once. Just use a basic low poo or basic cleansing conditioner, maybe have a clarifier on stand by. Plenty of product, plenty of massage, plenty of rinsing until your hair literally feels 'squeaky' clean.
I'm a little confused as to why you think your hair needs to be moisturised, and why you have been going about it the way you have. Key ingredients for moisturising (adding or increasing water) is anything that acts as a humectant or is rich in humectants. I wouldn't call GBP that? And then a humectant free gel?
Be aware that water alone will 'moisturise' or soften hair, if you leave your hair wet for say ten minutes the water will start unravelling the proteins in the hair making it feel more conditioned. There is no benefit in using numerous conditioners one after the other, once all the places on the surface of the hair that conditioner sticks to have conditioner molecules on then you can't condition your hair any more without build up.
Hope that makes sense and has not confused you more!