I would be so sure. The Executor is massive
compared to the Ascendant Spear which is around the same size as a Star Destroyer. And with over 5,000 turbolasers the Spear is kinda outgunned... However, the Spear has a huge
advantage in terms of maneuverability. The Spear had a class 0.5 hyper-drive with 0 being the fastest and 6 being the slowest. While the Executor had a standard Class 2 and was a lot bigger anyway which would further impede its movement - basically its gonna be stock still in any fight. So that Spear can literally run rings around the Executor. (Consider this, the Spear has the same hyperdrive as the Millenium Falcon which made the Kessel Run in less than twelve parasecs
) It could easily dodge and avoid the Executor's attacks while making precise and hard hitting attacks like in the Battle of Endor and take down the Executor's shields - then all it takes is one blast at the command tower to take that thing down.
However the Spear would probably have the whole of Death Squadron to contend with... however 1v1 the Star Destroyers don't stand a chance, or any other ships. So all it takes is a bunch of Harrowers to keep them busy and the Spear can literally cleave its way to the Executor. But that's just my opinion.