A "centrist" who looks at each issue and takes the average of the mainstream parties' positions is a fool, and will be wrong more often than someone who picks a party and follows along with their beliefs.
Someone who looks at each issue and comes to their own conclusion is likely to end up with views that will not line up cleanly with any political coalition, and must choose which issues to compromise on when deciding which coalition to back in a given political contest.
A political party is a compromise - a bunch of people who've decided they can accept one-another's redlines and non-negotiables.
A sane person doesn't just choose a party and adopt their party-line; a sane person works out what their opinions are, and maybe then chooses to support a party with policies that are sufficiently congruent with their views. Or not.
People who don't think for themselves are not really participating in politics. They're kidding themselves. They should voluntarily refrain from voting.
Someone who looks at each issue and comes to their own conclusion is likely to end up with views that will not line up cleanly with any political coalition, and must choose which issues to compromise on when deciding which coalition to back in a given political contest.