The actual mid-high stakes stealth kings are druids. Find Familiar (cast before breakfast to recover the wild shape). Strong perception. Decent stealth, backed by Pass Without Trace. And the ability to shape shift into an animal.
I think a bard (built for it) is the true stealth master.
A Lore Bard can have Pass Without Trace, Invisibility, Glyph of Warding, and Arcane Eye by 7th level plus Expertise in Stealth and Perception. A Spell Glyph bypasses concentration with a little time and gold to allow Pass Without Trace and Invisibility at the same time.
They can also turn that into a group benefit. Glyph Pass Without Trace (it targets one creature, the spellcaster, and emanates from there}, hand out some BI dice, and upcast Invisibility to the number of party members. Group check with the BI dice.
Plus they can pick up a familiar too if they want.
We can do a lot mixing and matching spells with a Bard. The only issue is what they might be giving up to do it.