How can it be possible to finish bottom of the leaderboard and still get 2 points. The board at the end showed -
P&J 6 points
K&A 5 points
S&N 4points
M&A 4points
G&K 3points
A&A 2points

Surely the bottom 2 should get 2points and 1point.

Because there was a tie

It used to be as you say 2 years ago, but it led to a judges 3-3-1 semifinal when Tom on 1 could not be saved from the dance-off by phone votes. Tess issued the invalid invitation to "vote and save your candidate from the dance-off".

The dance-off had to be called off and BBC had to refund calls.

They changed the system after the series 6 semi-final debacle.

Although now that there's no dance-off, they should have reverted to the old scoring system, as it now gives an unnecessary boost to those below the tie. Ah well.

That is spot on.

A five way tie at the top would mean all of them getting 6 points and A&A getting 5. What "wizard" thought that system up?