I personally find flat bars uncomfortable, they hurt my wrists. the are not ergodynamic

definitely not as aero

Classic drop bars let you ride in multiple positions, including flat bar like should you choose this is super helpful, especially being able to go to the drops in a headwind

change bars will not change the bike geometry, to make changes you would need to make changes to stem also

if you are not comfortable, good is to get the drop bars so they are not slammed super low and go from there, next step is bike fitting