Thanks to everyone who contributed, there are some valuable insights here that will certainly help others facing similar decisions. Some insights from my side as well
As highlighted in the discussion, this decision ultimately depends on individual context, particularly:
Career aspirations: ESSEC does have a strong reputation in France for roles in market finance, thanks to its alumni network and ties with major banks. ESCP, on the other hand, offers solid international exposure, notably through its London campus, which could be advantageous for those targeting roles in the UK.
Use of the gap year: Taking a full year just to retake the GMAT may carry risk if it's not paired with other meaningful experiences. However, combining it with internships, a short academic program, or professional certifications can significantly strengthen both your profile and candidacy for more competitive schools.
School reputation vs. strategy: While school branding does matter, especially in certain finance circles—what you do during the program (internships, networking, electives, location choices) often plays a bigger role in securing the most competitive roles. ESCP can offer strong outcomes for finance-focused students who take a proactive approach.
There’s no one-size-fits-all answer. It comes down to your current profile, how confident you are in improving it over the next year, and what kind of return (in terms of career outcomes) you realistically expect from switching schools.