Hey, I know that battle against Tau!
It depends how competitive you want to get. If you want it less competitive, then get more shiny toys and less units. If you want more competitive, then dump the toys (including the purgation squad) and get more efficient units.
The purgation squad isn't really that good: 1) it's overcosted, 2) it's short in range, 3) you can't combat squad with only 9 and 4) the most important one....it's not a scoring unit and you have no way to make it scoring without a Grandmaster. I would drop this unit.
Here's an example of what I would consider a really competitive purifier list.
Crowe
Vidicare
ven psyrifleman dreads
ven psyrifleman dreads
5X Purifier, 2 psycannon, 3 halbreds, rhino
5X Purifier, 2 psycannon, 3 halbreds, rhino
5X Purifier, 2 psycannon, 3 halbreds, rhino
5X Purifier, 2 psycannon, 3 halbreds, rhino
5X Strike squad, 1 psycannon, rhino
dread psyrifleman
dread psyrifleman
dread psyrifleman
1985
You have 15pts to play with on upgrades. I would recommend swapping out 1 halberd from each purifier unit for a hammer and if you still have points left over, get searchlights.
Strike squad is for camping objective while Crowe takes their rhino. In annihilation, then strikers stay in rhino and advance with purifiers. Crowe runs behind a rhino and out of
LOS.