A first-rate student will excel despite the flying school.
An average student will do well enough in an average flying school.
A poor student will struggle no matter the quality of instruction. You can't make strawberry jam from pig****...
Occasionally you will know that if the applicant trained at school X under CFI Y they will definitely know their stuff, but that only ticks one box in a long list of requirements.
Choice of flight school is not a ticket to a perfect career.