Using a ranked ballot is not complicated.
Instead of checking off one choice, voters will rank from their favourite to their least favourite. We do this all the time: chocolate is my favourite ice cream, strawberry is my second favourite, and vanilla is my least favourite. This is the same, just with candidates for city council.
Cities that have used ranked ballots have found that people do not find using them complicated:
A 2009 study by St. Cloud State University found that 95% of Minneapolis voters felt ranked ballot voting was easy to use.
An exit poll conducted when Santa Fe, New Mexico first implemented ranked ballot voting found that 94% were satisfied with their voting experience, and 70% were very confident their ballot counted as intended (compare this to only 55% of New Mexico voters feeling that their vote would count as intended for the 2016 presidential election).
A study of two San Francisco ranked ballot elections found that “Voters of all races and ethnicities find [ranked ballot voting] easy to use.” This was based on exit polls conducted by the Public Research Institute at San Francisco State University, the Asian Law Caucus, and further analysis of ballots by Fair Vote.