Which "一條龍小學" you are referring to? If you don't want to disclose the name, is it a DSS? Because majority of one-dragon gov't aided schools are either band 2 or band 3, so switching to another school may not solve your expectation to have better allocation.
Moreover, the S1 allocation of a primary reflects the school on a whole but also affected by parents' choices. At the end, it is only the students banding which will affect our choice.
You mean "easier"? Well, honestly 17% are not a lot of seats. Also, it really depends on where the top students in the nominated primary schools would choose. If they all leave for other band 1 schools, then it will make room for the other band 1/2 students in the school.