It is a bad idea in my opinion to sell BTC and LTC to buy Doge, because almost every movement of the altcoin price increase is caused by BTC, and the new Doge price movement is supported by a businessman is Elon Musk, and means the rise and fall of Doge prices depend on him.
In general, it is true, everything is moving behind Bitcoin. But if it stands still, then investing in Doge is quite a reasonable thing, because with a stable market, Doge has the ability to grow, especially this has been clearly seen lately. However, it is difficult to predict the moment when the BTC will continue its movement up and down. Therefore, it is best to diversify your funds without relying on one thing.