Left vs Right is always a relative term... Etymologically it refers to the physical left-right split of parliamentary seats an hemicycle, from progressive to conservative in most (all?) of Western parliamentary tradition.

If members of a group/party always sit on the left side of the hemicycle, that party is, by definition, left wing. Sure, the same party in Belgium might sit on the other side, but that's hardly relevant in a local context, because that party doesn't vote in Belgian elections now does it? (And thank god for that, we've got our own insanity to deal with).

Now of course this linear classification has very obvious limitations and cannot possibly describe the entire nuance of each party (or even person)'s politics. But saying "literally everybody except maybe ten people I agree with are on on the other side of the center" robs the left/right distinction of all meaning it still holds. Placing the center "just right of my personal politics" will not make the conservatives magically go away, it just makes political analysis less meaningful because everybody's got their own idea of the center now rather than using the median congressperson as a handy reference point.