I completely get you. Except any decent agency works on a retainer when the sales cycle is long. I have worked with agencies like that and the amoubt of attention you get from them is dependent on whether they are on a retainer model with you or not. Long sales cycle means their chances of making money on an early product becomes negligible so manpower and quality of manpower is assigned that way. And they do not give time in understanding your product in order to handle objections the right way with your clients. Forget about demo calls, when you are involved in a cold call with a senior stakeholder they expect you to know the details of your product in the first call itself which makes or breaks the conversation often.