He had been rushed through training to specifically kill Darth Plagueis and still ended up dead.
Besides the Jedi Exile is also a master of numerous lightsaber forms and has top tier speed feats herself, any lacking on her part is balanced by advanced precog.
Also this arena is one Surik is very familiar with, I can see that being an advantage for her.
The first two really didn't matter. It's not like he had some free first strike. The latter two are basically synonymous - he knew Plagueis' form in and out. Venamis himself used a wide variety of forms, none of which were stated to explicitly counter Plagueis' form, so that's just you trying to magnify the number of advantages Venamis had.