Milly,
Why would you even use a term like bog standard… although I’ve heard the term used multiple times before, it just sounds derogatory or dismissive. I might be wrong but you seem to be a disheartened by something, and you’ll need to overcome this feeling to be able to respect your profession. Once you find the right reasons to start respecting it yourself, others will respect you and your choices as well.
To me, there’s nothing ordinary or mundane about teaching at all - no matter at what level. As far as intellectual capacity is concerned, I agree with poppies in that it’s really up to the individual to advance and excel in any direction that they determine to be pertinent to their career goals. Even in the most basic of subjects, there’s always something new going on - pick up a field publication and find out. Furthermore, there’s always novel pedagogical strategies and tactics to try out, and always opportunities to involve yourself creatively in the development of your students. Finally, you can use your experiences to shape the learning for teachers of tomorrow - publish articles, find stints at teacher's colleges etc.
Teaching is not quite a stagnant profession per say – it’s just what a teacher makes of it.