In order to improve,is it better to go random or pick civ?

I've always believed that going random was the better way to improve because by playing unfavorable matchups it would be better for improvement.

But in Asia it seems that everybody picks civs and every game is s tier civs with the occasional a tier.

My elo has just stagnated since the last 70 games and I've lost about 100 elo in the past week.What I've noticed is that some days I'll get decent civs and gain elo,and lose it all again on other days on which I keep getting Goths and tatars and Portuguese.

This feels so discouraging because my performance seems to be luck based and my elo is going nowhere.

Half my games I'm thinking about what I can do to win this unfavorable matchup over actually improving my gameplay.

So if you just pick civs and gain elo,do you really improve or just abused the civs to gain elo?