The front carry is the only odd bit as far as I'm concerned.
I regularly back-carry my 20kg 3yo in a sling (Toddler Tula, if you're interested - note the word TODDLER, so not a sling intended at all for babies). If anyone has any tips to 'just make him walk' when he's tired and/or in a strop and won't move, I'd love to hear them! I can't put him in the pram anymore - his feet drag on the ground because he's so tall.
I have been known to stick his 5yo (tall, rake-thin) brother into the same sling if he's being particularly obstreperous about getting a move on, or refusing to move. The same child did 6 miles around Paris in one day on foot, so I'm not remotely worried that I'm stunting their independence thanks.
I can also say with some authority that it's not bad for your back (I'm an OT working with patients post-spinal surgery). A decent ergonomic sling is a far better way of carrying a tired child than on shoulders, hip or piggy-back which I'm sure all of you throwing your hands up in horror at older children in a sling have done on many occasions. Pushing a pram isn't that great for your back, FYI, especially double or heavily-loaded ones. Carrying additional stuff like balance bikes and scooters that your child isn't using, that you've taken out because you can't POSSIBLY put them in a sling if they won't walk, is also not great for your back. So that argument does not wash, sorry.
For the record: I'm 5ft 6in, 60kg, not pear shaped, haven't a grey root in sight and can't remember the last time I wore a skirt.
There are some rude, judgemental fuckers on this thread.