Afaik, brushing your teeth doesn’t weaken the enamel or anything like that, or at least it shouldn’t. When brushing it’s not actually the bristles that are supposed to be doing most of the work, it’s the toothpaste which acts as polishing paste (it has tiny little micro abrasive particles or something like that). So if a dentist ever asks you what kind of toothbrush you use, soft, medium, or hard bristles, if you answer anything other than soft they’re probably going to recommend switching to soft bristles. Medium and hard bristles can damage the gums and with hard enough brushing overtime can be macro-abrasive and wear away your teeth. Better to use soft bristles and let the toothpaste do the polishing work.