I changed from secondary as a HOD to primary 9 years ago.
Initially the was more creativity. Now, if anything, less than secondary. It has become the same exam factory that secondary was when I left, more so.
My marking load is way heavier. I have 35 in my class, no TA. Maths and english have to be marked every day, topic every other day, guided reading, spelling and grammar also. That's a load more marking than I ever had in secondary. Plus it all needs to be responded to, every day. Plus homework.
The pastoral side is way more intense. You see parents all the time and you are far, far more involved with the child welfare than you ever are as a form tutor.
Your class will have more SEND of more severe nature. I always thought I coped pretty well with the challenges at secondary but i was gobsmacked initially by what primary teachers coped with. The high threshold for diagnosis and echp means you will have children that are not yet at threshold but will be by secondary. Many finally attain special school places in year 5 / 6 / 7. Expect to plan for children still on the p scales even if you teach year 6.
Although the hormones haven't fully kicked in yet, behavioyr needs managing more. A lot more. And you won't have a unit or space to send the kids not behaving to.
The planning is scrutinised far more.
When you have one class in a possible one form entry, you carry the load for whole school performance, especially in 6. The targets are often ludicrous.
In.secondary i did one break duty, one toilet duty. Now i do two breaks and have to run 2 lunch clubs. I also run 3 lunch interventions and 2 after school interventions because I have no TA.
Then I have to do the huge production every year too.
I am actually thinking of going back the other way again. I have kept my hand in A level marking so I could do it. I do love my class each year but it's far more onerous and exhausting than secondary was, for me at least.