TanteStefana2, it is pretty well explained in many places that isn't true. Any coin that employs mixing wlll have essentially the same bloat (linear factor expansion of transaction count and/or size), except that the base transaction size in Monero is much smaller than in Bitcoin, so even after applying the relevant multiple, the size may still be smaller. DarkSend specifically suffers from the same bloat as Monero, or worse, in terms of using standardized output denomination sizes (some other coinjoin-based systems don't do this and have other problems).
Dash has fewer/smaller transactions (by smaller I mean making paying fewer payees) on its chain, and many, many fewer using DarkSend (the latter is probably the bigger factor). That is the only reason it's chain is smaller. There is no fundamental technological difference at work.
With Dash it's a choice, that choice has kept our blockchain smaller. In the near future, most wallets won't be using full nodes. Yet, they will still have the security of their wallet's information due to the distributed way the information will be downloaded through the DAPI, served up by Masternodes quorums. Masternodes, being compensated through the system, can afford to run with terabytes of storage. Yet, the Masternode network is fully distributed throughout the world and there are Masternodes on every continent.
*If* the new version of Dash has masternode blinding, there will be no need for multiple mixing sessions. This will speed things up. There is a lot of room for improvement, but our team has constantly made great progress. After reading this thread, I have no doubt that one should stay as far away from Monero as one can. In fact, I think this will be the last I say on the matter. Say what ever FUD you like after me, I won't respond so enjoy.