Having the mizzen has several advantages:
1) It allows you to balance the boat
more effectively as you have more choice of where to place your center of effort (the average of the forces produced by your sail) in relation to the center of lateral resistance (the average of the forces generated by your keel
and rudder), which allows you to sail more efficiently on any given point of sail (except upwind, where sloops generally have the upper hand).
2) It lowers your center of effort. Ketches (and yawls, but less-so) can generally have shorter masts compared to a sloop
with the same sail area. What this means is 1. Your rig is inherently stronger (because the horizontal component of the force on your shrouds / chian plates is greater owing to the more acute angle of the shrouds with the deck) and 2. Because the average of the forces acting on your sail is lower down you will have less heeling moment.
3) It breaks up the sail area into manageable chunks, which is great for short-handed sailing. It also makes it much easier to reduce sail area in a hurry when the breeze picks up; something that if often a pain the arse for sloops with big slab-reefed mainsails. Consequently a lot of people will reef the jib
(because it roller-furls) when they should really be reefing the main, and this leads to poor performance and an unbalanced boat.
As previous posters have said, try sailing under mizzen and jib alone in anything other than a very light breeze. If you're under full sail, the breeze picks up and you start to get weather helm
, flatten the sails
first with the vangs, halyards and outhauls and if it's still a problem ease the mizzen sheet a touch or better, go down on the traveller if you have one.
I'm confident that in time you'll come to love your ketch.