Ah well slate is a whole different matter. That has the potential to look really good - I did wonder if it was something better from the previous pictures. I agree that the trampoline which has landed from outer space (we have one too!) should be tucked away, and probably leave hardstanding underneath, because having one on a lawn has peculiar effects on the grass and you end up with a series of Olympic rings across the area where it has been at various stages.
I do believe that you have done lots. I would say that of all the time I have ever spent in the garden, only 15% at most would have been spent on growing plants - probably 10% come to think of it. Garden jobs for me have included cutting up an enormous old style metal oil tank with an angle grinder with metal cutter blades - it was firework tastic - to get it through the house for collection by a metal collector. And shifting vast piles of earth, taller than me, which I WISH I had photographed, which were covered with weeds - the 'hills o' weed' as I called them. That was because we had the topsoil from the front dug out and redeposited in the area out the back, but it took a couple of years to get round to it. Included was a dog skeleton, which someone has lovingly wrapped in a loosely knitted jumper for burial, and after the diggers moved everything, and I barrowed it, I am still turning up dog bones and bits of that jumper, and horse teeth, and sheep mandibles, and all sorts (this was a vet's practice outbuildings).
We have sorted out three skips worth of rubble and sick soil, redistributed hardcore that we bought and didn't need, transported stone down the paddock. Then built the stone and brick beds out of what we had left over, designed arches out of discarded farmyard wooden poles left on site, built a gazebo - our builder did the woodwork but I did the brick supports, put up a fence, raised beds, a greenhouse. And this has taken nine years, and I am only just about to plant things in actual real soil - not raised beds. So I totally get your meaning when you say you have done loads, and I suppose all that explains why if I were you I would get rid of the concrete. It is because I believe in stripping back and building what you want from scratch. All the time that concrete is there, you are bending your own plans round something that someone else put there, which will have a serious impact on what you want to do, and your possibilities for the future. Even if you get rid of it and have to put down a temporary solution, without it, you are back to basics and can do what you want. Also, having some of it removed will reduce the risk of flooding as it will allow for greater absorption. If you had that tree chopped down, then less water will be being sucked up by roots. You will have such fun with your little girl in the greenhouse once the glass goes in!!