Gross Negligence

I was hired as a manager for a BPO last 2013. After 6-7 months I got transferred to a different account with a new team. One of the biggest program I handled only has 1 staff and due to understaffing there were a lot of mistakes. I have asked my boss for additional staff and a supervisor to overlook the staff members as early as October of 2014. The hiring began late and a supervisor was only added Jan 2015. Prior to that I was trying to manage the training of the new staff, holding the fort as both manager and supervisor and correcting the past mistakes of my old singular staff. I was eventually put into a performance improvement plan last Nov with end date of Dec 19, 2015. The escalations and issues continued tho until I was given an NTE earlier for gross and habitual negligence citing items and responsibilities normally handled by staff members which I ended up owning due to lack of staff and delays in hiring for a supervisor.

Can this be considered gross despite not having the full support and help of my vertical in making sure I'd succeed in my position by not providing me with the needed staff members which forced myself and only staff to take more workload which resulted to problems?