I'm confused by the Sidekick rules in Tasha's Cauldron of Everything. In the "Gaining a Sidekick Class" section, it says this:
The sidekick's proficiency bonus is determined by its level in its class, as shown in the class's table. Whenever the sidekick's proficiency bonus increases by 1, add 1 to the to-hit modifier of all the attacks in its stat block, and increase the DCs in its stat block by 1.
So when I'm building a level 1 sidekick, is the listed +2 proficiency bonus considered two instances of "proficiency bonus increases by 1", or is the creature considered to already have a +2 bonus, and only gets to upgrade attacks and saves once it reaches a proficiency bonus of +3 on the relevant sidekick class table?
As a specific example, a Bandit has a Dexterity bonus of +1 and his two attacks (scimitar and crossbow) both have a +3 bonus, implying a pre-existing proficiency of +2.
So when he becomes a sidekick and gains a level of Expert, do his attacks still have a +3 attack bonus or do they suddenly become +5?