I dont think its wonky at all, your slight of hand is what is used for Thieves tools. So for example if your going to remove a trap, pick a lock your going to use slight of hand and your proficiency mods to apply to the DC.
Scott
Sleight of Hand is not what is used for thieves tools. Tool proficiencies are not tied to any single ability score like skills are, and they are not used when using a skill. Tool proficiency cab be tied to any ability score as the DM sees fit. So removing a trap is proficiency + DEX, which can be different from a rogue's sleight of hand bonus if the rogue is proficient in one but not the other or has expertise in one but not the other.
In any case, the player only applies proficiency or expertise if they have it for that tool, and if the player does not have it, in many cases they cannot use the tool and hope for success.
Removing a trap: thieves' tools + DEX
Convince a potential employer that the rogue is the thief for the job: thieves' tools + CHA
Play the lute: Lute + DEX
Appraise a lute: Lute + Int
Win at dragonchess: dragonchess + Int
Bluff to convince opponent to draw at dragonchess: dragonchess + CHA
The important thing to remember is that the tool lets you add your proficiency or expertise to an ability check (
not a skill check) while using the tools.