There are many applications from third party without advertisements. Dig around a little before blaming the company for not developing their own application. This is 'stock' experience. That said.
I hope you have initially selected SD card as 'External / Portable'.
File manager - Solid explorer , Fx explorer , ES file manager.
Gallery application - QuickPic
Also, the default stock applications can be 'Disabled' . It's similar to uninstalling it.