YABVU
Surely you have the imagination to figure out that everyone has different children/coping thresholds/family set-up/health situations?
There is also the fact that your oldest child is in school, which effectively means you have one child to cope with for a fair chunk of the working week. That's very different to someone with a 2 year old and a baby, for example.
I have a 3 1/2 year old and a 1 year old. DP works away at least 4 nights a week and I work 3 days and squeeze some freelance work in around the kids. I find it hard going. Yes, I can manage bedtime/bath-time/meals on my own, but when I do have another pair of hands around it makes things much more pleasant.
For example, DS2 tends to wake around the time I get up for work and will quite often start screaming blue-murder to be got up. So I'm trying to sort out breakfast for DS1, get myself dressed, get DS2's milk ready to a backdrop of hysterical screaming - this does not make mornings restful. Add to that the fact that DS2 has usually done an epic poo which needs sorting before breakfast, while he thrashes and wails because he's hungry, and the fact that DS1 will be yelling in the background that he can't find his spiderman t-shirt, it's a wonder we actually leave the house at all!
When DP is home, the morning is positively pleasant.
The swimming thing - I've only recently started taking them both on my own because I've found a pool that has no deep-end and DS1 is confident enough to splash about while I tow DS2 around with armbands or in a seat. Getting ready afterwards is still pretty stressful though.
Having said that, I do know some people who simply choose not to cope alone. It's not that they can't - it's that neither of them want to. They simply don't like looking after their children alone and will guilt-trip family into helping out so that they can do other things. But that's slightly different - it's more a case of trying to get out of looking after their children at all, never mind single-handed.