Sneak is OP. You just have to keep in mind how it works.
If you stay out of vision cones, you literally never have to roll a stealth check. You can do whatever you want, even in full plate and no-one cares.
The trick comes to when you have to pass through a vision cone, in which case you will have to pass stealth checks every so often. Which, especially at early levels, can be hard to pass consistently. Which is where invisibility comes in handy if you need to cross into vision cones.
Later in the game you get access to items that help (Such as the robes of Cats Grace from the woman on the path to the Creche which gives advantage on all Dex based skills, including Stealth) as well as more ways to gain invisibility for those times you can't avoid vision cones (There's 2 different rings that provide it, plenty of scrolls and potions that provide it and certain subclasses like Gloom Stalker and Thief end up getting spells that provide it)