The plateau you're hitting is actually pretty normal, and it's not really about doing it "wrong" - it's just how the mechanic scales. Your success chance is based on a formula that weighs your Pickpocket skill against the target's level and the item weight, so even at 60s you're still going to whiff a lot on higher-level NPCs or heavy stuff.
The perks matter way more than raw skill though. There's one early on that boosts your success chance by a flat percentage, and then later there's one that makes pickpocketing items from people way easier. Those two alone will feel like night and day compared to grinding without them. There's also the one that lets you pickpocket equipped items, which opens up a ton of options if you're going for specific gear.
On Switch you're stuck with vanilla, so no mods to help you here, but honestly the game's designed around this grind. If you want to level it faster without the tedium, just target light stuff on low-level NPCs - gold, potions, lockpicks. You'll hit 90+ eventually and yeah, it does get noticeably easier, but the perks are doing most of the heavy lifting, not the skill number itself. Usefulness-wise it caps out pretty quick once you have the key perks, so don't feel like you need to min-max it to 100.
