I would like to know if the expression I TAKE YOUR POINT BUT... can be used in a formal letter. Thank you in advance
Yes, I can imagine using it in a formal letter, e.g.
1. On the question of the revised pay structure, I take your point; but I wonder whether you have fully taken into account the effects of closing the pension scheme to new members of staff.
However, if you need to be particularly polite in your letter, you might want to consider a more oblique alternative, e.g.
2. On the question of X, I fully accept that Y. However, I would suggest...
All the best,