Well, all you have to do is go out and beat them so they don't get more CP than you to qualify over you for Worlds and there, no big deal.
And honestly, I'll also make the case that Seniors, especially at a high level like Nationals top cut and Worlds, is very close to, if not just as difficult as Masters. Most of those players are close to being old enough to be in Masters anyways and their brain is just as developed so they play pretty well. They can netdeck and/or build decks just the same as any of the rest of us. Sure, they don't have the big name players that Masters does, but it does take a lot of skill to win.
The main difference is the amount of players in Masters as opposed to Seniors. That is rather obvious as the Masters age group encompasses a LOT more players than Seniors does as the Senior division only includes 4 years while Masters includes (realistically) about 40 years. This is both a positive and a negative. With less players, there's a statistically better chance to win. However, with more players, you have a bigger top cut. And anyone knows, once you make cut, anything can happen.
TL;DR - Seniors is hard too.
But don't get me started about Juniors. That's not even close.