It is possible to buy a thickier pen. Booxtor sells them. Or someone has suggested to incorporate default pen into thickier ball-pen.
Concerning erasing and writing.
If you speak about Scribling application and not scribling to the text, there is an alternative Scriblin App developed by PeterX at this forum. It might suite your needs better than Onyx one. For example the eraser is like real eraser, so no problem with 'i's dot'.
https://www.mobileread.com/forums/sho...d.php?t=170271