Again, just get a spellcaster who can concentrate on Enhance Ability: Dexterity (Cat's Grace) and suddenly any fixed bonus is better than another, redundant source of Advantage.
Since Enhance Ability is tier 2, and Bard, Cleric, Druid and Sorcerer can cast it, thats doable from very early on.
So no this is doable with level 3 characters already.
Of course what you otherwise really want is a Rogue with level 10 (guaranteed minimal roll 10, thus also no chance for Critical Failure), Sleight of Hand Expertise (+8 for level 9+), Dexterity 20 (+5), Guidance (+1d4) and Bardic Inspiration (+1d10), and really any other item that can push the skill.
And in the end you always have Player: Reload to fix mishaps of course.
It's unnecessary to waste a spell slot for Enhance and even worse maintain concentration, when the gloves are literally a piece of equipment that provide free Advantage that one can easily swap to before doing any stealing, which is what I do personally. I have the ring and the gloves for Sleight Of Hand placed in the Custom hotbar, ready to swap to and from any time I intend to pickpocket someone.
It's as intuitive as it can be, which allows me ease of mind by not depending on a limited spell resource and concentration. So to me personally there is no point in using Shadowheart or any other spellcaster to waste spell slots and depend on them when it's just a simple matter of swapping the gloves/ring on the hotbar. Plus I already use Shadowheart's Enhance for Charisma checks so it's not an option, while Guidance I gain from the Harper amulet equipped on Karlach.
I care about resource management and not resting every 5 steps of the journey, so I play this way. My pickpocketing checks constantly roll between extremely high 30-37, so that +1 from the other gloves is not even needed.
