In Bitcoin, Litecoin et al, 100% of the blockchain reward is "spent" on maintaining the difficulty level across all blocks. (The clue is in the word reward. It's not a gift, it's a receipt for the miner's contribution to increasing the value.opening price of the next block by making it more scarce).

In Dash, only 50% is spent on maintaining the difficulty level and the other 50% is "spent" on masternode rewards (as you will know, being a recipient). That capital does not go back into the chain as it would do with mining rewards. (i.e. it does not get spent on raising the difficulty). Instead it leaves the chain completely and these coins emerge with an opening price of zero. (i.e. they arrive in the hands of the holders at a price of zero).

So the coin flow "out" in a 100% mined coin is:

from blockchain --> miner --> market

and this is balanced by an equal and opposite capital flow in dollars that goes:

from market --> miner --> blockchain....in the form of a difficulty contribution which establishes the opening price of new mined blocks.

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However in Dash, the coin/capital flow is split:
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from blockchain --> miner --> market (these coins have a costbase which equals the mining cost)
from blockchain --> masternode --> market (these coins have a zero costbase)

and this is balanced by 2 equal and opposite capital flows in dollars that go:

from market --> miner --> blockchain....in the form of a difficulty contribution
from market --> masternode --> END....and exits the network here as this is used to fund pure profits which do not benefit the network.

Note that none of this depends on anecdotal appraisals of "who sells how much" or even whether coins are sold or not. The fully mined blockchains charge for ALL their blocks whether the initial holder sells into the secondary market or not.

This is the only fundamental systemic distinction we have with 100% mined competitors and goes a long way to explaining why we suffer a chronic and continuous decline in ranking year after year by comparison, even though we may have far more interesting end user features.

There is a huge cost borne in paying those idle masternode rewards across 5000 nodes. (Currently running at half a million dollars per week). The cost is felt in loss of marketcap from the chain.