Ok so I'll be totally honest here and this is my own experience. My gap was 2 1/2 years. My first DD was toilet trained and had been weaned off her dummy and was sleeping in a bed at this point. She was also an excellent talker. So we tried to make things easier by making sure we only had 1 child in nappies etc. It should be a bit easier with a 4yr old though.
It probably depends on the baby to a degree but overall it is much harder having 2 than 1. Basically either me or dh always has a child to deal with. Often they are both on top of me getting cuddles 😂 You don't get much or any time to yourself.
I found it incredibly hard. Especially in the first few weeks/months. Baby wasn't sleeping much at all maybe an hour or 2 at most at night. Then I'd be expected to look after a demanding 2yr old all day. I was utterly exhausted. I ended up going to bed with toddler at 8pm and dh wld look after baby and do last feed. That meant that I was at least getting 3-4hrs of solid sleep.
Baby got chicken pox at 10wks old and 2yr old also got them and it was awful! Baby was ok with them it was pretty mild but 2yr old was awful she was so ill and I had to call my dh one day to come home from work asap as he was supposed to work late but I told him he had to come home. Baby was getting the bare minimum it terms of care and attention as 2yr old was so ill.
Youngest is 2 now and it's a lot easier now but still overall hard work. I feel like I'm always doing washings and the house is forever a mess. I tidy and clean up all the time. However if I'm busy cleaning they are busy pulling toys out and making a mess, spilling things etc.
I also play referee a lot having to dash through from doing to dishes to stop fighting 🙈 My youngest is a bit of a terror she nips, scratches, pull hair etc thankfully rarely bites now.
It is also lovely to see them playing and cuddling. As much as they do fight sometimes they also cuddle and cosy up to each other.