He's not getting used to the premier league, he's getting used to a completely different set of tactics, instructions, teammates, a new role within the team.
How long did it take Otamendi to get playing his best under Pep? Aguero? Sterling? Even KDB said it took a long time for everything Pep was telling him to sink in. They didn't have to get used to the league, they'd been here for longer than Mahrez, Aguero was already a premier league winner, did that stop him from having trouble adapting? No.
It's not about favourites playing or not, it'll be a meritocracy, but anyone thinking Mahrez will waltz into the starting XI and start nearly every game like KDB/Silva/Walker/Fernandinho did last season is completely kidding themselves in my opinion. Attacking in this City side is a very precisely orchestrated operation, a lot of it revolves around knowing the runs and passes your teammates are going to make as well, so it'd be jaw dropping if he slid in seamlessly. It'll take time for him like it did everyone else.
If you really want to resort to personal attacks, we can, but I'm not sure why you'd feel the need, especially considering how the last time you complained about me was when in the Sterling thread when you said, what was it again? Oh yeah -
How'd that prediction work out for you?