I feel for you, OP. Parenting a 4yo and a baby is challenging, and we're all human - there are none of us getting it right all of the time.
I agree with @Triffid1. Different approaches work with different children, it's never a "one size fits all" solution. Maybe a time out/naughty step type of approach just isn't what works for your DS?
It's been a few years since I've had small DCs, but there's only 13 months between my ds2 and dd2. Ds2 was so sensitive, a mild telling off would leave him devastated. Whereas, even a big telling off would be water off a ducks back for my defiant dd2. I had to adapt my approaches to suit their very different personalities.
Looking back now, I do wish I'd worried a bit less about how I handled these situations. When I had my first, ds1, I was quite young, a single parent with no support or experience. My parenting wasn't great if I'm honest. He's an adult now - very well adjusted, hard working, and an all-round delight (if I do say so myself
).
12 years later, I had my last dc, dd2. I was much more informed, stable in a happy marriage, and had a good support network around me. She's been the most challenging of all, I'm definitely winging it and just getting through it whichever way I can.
You're clearly a loving parent, because you wouldn't be thinking/posting about this if you weren't. That's the most important thing, and I'm pretty certain you won't go far wrong 