The rate up for Sarisse totally sucks! It might actually be worse than a normal banner.
Normal banners, you have a 0.5 percent chance of getting the rate up unit. Then if you whiff on a rainbow, every 10 rolls gets you a 0.5% increase in 5* rate of which 0.0625 goes to the rate up adventurer. So after 1 10 roll, Sarisse's rate is 0.5625%.
For the gala, its initially also 0.5 % chance of getting Sarisse. The pity rate also goes up by 0.5% each time, but now Sarisse gets only 0.04% of the boost! To keep it proportional most of the pity rate boost is going to non-featured adventurers, dragons and wrymprints. Plus due to the higher rates for everything, you are likely to get pity broken even earlier! So after 1 10 roll, Sarisse's rate is 0.54%.
In short, if you just want Sarisse, this is a bad thing. If you are ok with other 5* adventurers and dragons, its still okay.