The market volume data gathered from exchanges is misleading as we cannot ever know what's going on behind the curtain (that's OTC trading). I wonder how volatility % would be if we knew all the trading going out outside of our reach.
I don't doubt for a second OTC volume has only been going up in the past few years. I know there were some recent news of a 144k buy which then was supposedly debunked, however this doesn't mean huge buy orders aren't happening OTC, and all of that data we cannot track so the analysis is always incomplete.
Eventually OTC will dry and whales will be forced to enter exchanges, but until then we just can guess.
As far as I am concerned, what is going on in the market or on exchanges is just what I see as a strategy to keep holding the price to some level so as to achieve the accumulation phase, which we all know that the amount most institutions will be purchasing to get in is not something they will basically be doing on any exchange as that could have a huge effect on it.
Basically, most exchanges put together will not even be able to hold up the volume, so in a way, I believe like you said, they will basically be accumulating the OTC way and keep acquiring as much as they can, while suppressing the price for as long as they can. The funds are there to do all this effectively and it has been their game, so they basically know how to do it well.