Has it always been rubbish at drying, or gotten worse over time? Our old dryer deteriorated over two years until I had a chap out to fix another bit of it. He cleaned out loads of fluff that had escaped through the filter and spread all over the innards of the machine. It was much improved after that and I bought a new and better-fitting filter which maintained the performance.
I prefer to line dry though, as the tumbler tends to shrink stuff (and the kids are not great at removing untumblerables before moving to the next machine). So I hang it out most of the year round and finish in the tumbler. I have a rotary airer that stands up on legs instead of plunging into the ground (from a caravan supplies shop). This means I can move it to sunnier spots and also bring it inside when going out or when the heavens suddenly open without having to unpeg it all. When it's very wet, I put the airer in the bathroom (window ajar) overnight and then finish the damp stuff in the tumber in the morning.
I have had several washer dryers, and mine have all been good. Are you using the longest possible time? They do take ages to dry stuff - doesn't mean it doesn't work, just that it is slow. My current one supposedly has a sensor, but I do find if I fill it then I need to put it on maximum "cupboard dry" regardless. With the crumpling, I know it is a pain but it makes a huge difference to wash, take everything out, give it a shake/snap, put it back in and put on to dry.
You can't dry a full load in a washer dryer. Need to take out washing, shake out and then return 1/2 to machine. Then remove straight away once cycle finished, shake and fold or hang. My experience with washer dryers is that they are not good for regular use, just the odd emergency or to finish off line dried.
I have a washer drier and always have to split the washed load in half to dry it. I put each one on for 90 minutes and have to take the clothes out as soon as they are dry and fold them up. Just realised my machine is on for four hours for every load of washing I do!!!
The first washer I had when I left home was a washer dryer. Like others have said, it took hours to dry anything and creased everything up to hell. It was forever shrinking things too and got ridiculously hot.
Best part about leaving that flat was being able to buy a separate washer and dryer.