With the goal of achieving climate neutrality, many European countries are accelerating the electrification of the transport sector—one of the major contributors to CO2 emissions. To reduce costs and improve sustainability, they are increasingly integrating electric vehicle (EV) fleets into the power grid. However, this integration introduces challenges such as increased pressure on grid stability, making coordinated charging strategies essential to fully realize the benefits of EV deployment. To address the EV fleet charging scheduling problem, this study develops a centralized optimization model based on Mixed-Integer Linear Programming (MILP), a widely adopted and flexible approach. While existing research typically focuses either on cost or emissions, and often within the scope of a single-country case study, this paper presents a comparative analysis of both cost and sustainability outcomes across five European countries: Croatia, France, Germany, Sweden, and Poland. By evaluating smart charging potential under uniform operational assumptions, the study highlights how the effectiveness of EV integration varies significantly depending on national electricity market structures and energy mixes. The results provide valuable insights for policymakers, energy planners, and fleet operators, demonstrating the importance of tailoring EV strategies to specific national contexts.