In terms of the old newborn Vs toddler, for me I disagree. I genuinely found babies ridiculously easy, and toddlers tricky. You've only got to look at photos of me with make up, decent hair and energy when I had a baby, Vs mum bun scraped bad hair and exhaustion a year later.
But my children slept better as babies than as toddlers. I wasn't particularly sleep deprived when I had babies. I woke hourly plus juggled work when I had toddlers. I remember referring to early maternity leave as a holiday at the time.
They weren't magical unicorn babies. They woke. They cried. One was very colicky, one struggled with weight gain and I was triple feeding for a while. But they couldn't answer back, they stayed put, and their needs were simple. I'll personally never understand why people find babies particularly hard. I find them a very gentle introduction to parenthood. Almost a halfway house. I think birth hormones probably play a big part. I was very fortunate with that, not even having baby blues, let alone pnd. I imagine wtf those it would be much more difficult.
Toddlers I found fascinating but brutal. I've never been so exhausted, and then they're all go during the day as well. They are constantly finding ways to try and kill themselves.
Perhaps for many it gets easier there. A mixture of disability and SEN means it got easier, but only by a bit. At 7+9 I still bed share with one. The other doesn't go to sleep till nearly 11 and is quite full on. My only child free time (apart from work) it's 11pm-6am, and that's usually disturbed by them still. Helping them manage and regulate their emotions, especially when life had thrown them curveballs isn't easy. Due to disability, I'm so doing a lot of personal care, but cognitively they are ok, so that brings a lot of psychological issues to deal with.
Our situation is unusual, but most of their friends have other issues. Many of my eldests friends don't sleep through still at 9, and sleep with their parents. I'd have thought that was nuts a few years ago, but they've all got different reasons, because life is pretty complicated.
So the amount of older kids who everything is straightforward for seems to be in the minority. But a straightforward school age child Vs a toddler, I wouldn't be surprised if it's easier. I just wouldn't know.