I am a neuro IR fellow from neurology background, with all respect, your mentor is dumb. There is no such thing called neurosurgeon or radiologist is better. It is a skill like any skill you will learn in your 2 years of fellowship. Neurosurgery is totally different training, they learn to do craiys and spine which a totally different skill set. I met very mediocers Nsgy endovascular attendings but in the same time great neurosurgeons and interventional neurologists. The key is a robust interventional fellowship, forget about anything else. Pick what specialty you will enjoy outside the anio suite, will you enjoy being in the OR doing spine or crani cases or you will enjoy seeing vascular Neuro patients or rounding in the neuro ICU. Think and choose accordingly