I wonder what might have caused such a great change in the couple of months for people to stop endorsing XMR as much as Dash.
I understand that D-coin has a very limited supply due to politics of rewarding only early adopters, and punishing miners with low rewards, thus pushing higher prices and more interest around that.
With Monero nothing changed. Monero is doing as was in last 2 years steadily, without any hype progressing. It is a tough road since was never walked before.
About DASH, is one reason you mention. Since few people hold most coins is much easier to manipulate on market. And market is thin. That was already happening in last 3 years, so nothing new. DASH had high price before no matter that no one used it since was just BTC clone with nothing that will be impossible to do with Bitcoin.
But there is other thing. DASH have PoS, so this few intaminers get most of 45% freshly issued DASH. That is now close to $15 millions. Since they hold most now they get this for free. every year. They dont need to pay electricity So you can imagine they can afford a lot for this. Let your imagination play here.
Then there is another budged. 10% of all issued DASH, that is mostly used for advertising. People make youtube videos, ..... Those 10% are now $3.5 millions.
This is what happened. I am not sure if Bitcoin have $10+ millions marketing budged. For sure no other coin does.
PS: Your title is misleading. Normally people would understand technical comprising, and this 2 coins are quite different. No should maybe edit it to a bit to what you asked in OP. [XMR] Monero vs [DASH] Dash -
Price and Avareness Comparison