Nico is not as good a driver as Lewis. That much is very apparent. If the skill of the driver made no impact, Lewis and Nico would be a lot closer than they are at the moment, and there wouldn't be half a second between them in the final sessions of qualifying.
Ferrari are being plagued with small issues on most weekends, like the poor choice in strategy this race, power failures and things in previous races, but Seb is obviously a much better driver than Kimi, even if they are very close in points. Seb has been getting more top 5 finishes, but Kimi has been more consistent as of late.
Without going through every team like this, it is clear if you actually look back through the results of the last few races, that while Mercedes have been on top, the rest of the spots have been pretty much up for grabs for anyone. Red Bull, Lotus, Williams, Ferrari, all getting podiums. Renault powered, Ferrari powered and Mercedes powered cars are littered across the field, and below the top two, you can't make predictions how things are going to end before the race weekend starts.
I think F1 is currently very unpredictable. There are a great many things that can change the structure we have at the moment, and a lot of things that can impact the firm footing Mercedes has at the top. But to say that the skill of the drivers has no impact on the final race standings, is largely false.