BTW my seatpost qr needs to be very tight to stop the seatpost dropping.
I had a number of issues with my bike, including the sliding seatpost. All were sorted out by the dealer at no cost.
The seatpost clamp is not the best but the issue is the post itself. My post kept sliding down too. I clamped it up so hard in attempting to keep it still that the clamp broke. The replacement clamp was identical so didn't fix the problem.
Genesis supplied a replacement post of the type fitted to the more expensive bikes and it solved the problem instantly, the post stays put with far less clamp pressure. The original Altitude 00 post is an extruded tube, so is very smooth. The replacement tube have a machined/turned outer surface, that's all it takes. The frame then has something to grip on.
The way the barrel on the seatclamp is countersunk removes a heck of a lot of thread, which is why it can fail if you really crank it up.
Is the Core 10 the geometry same as altitude ?
Yes, I think it is, and a couple of pounds lighter.
only a few niggles to do with the wheels (not great quality), and tyres (Conti Mountain Kings, puncture city maaaaan!)
These bikes seem to be very much set up for off road. The tyres are really good off road, I've never had a puncture, but I do run quite high pressures in them. I think it's a case of setting the bike up for what you're going to be riding on.
I've replaced the wheels with Mavic Crossride for off road use but the supplied wheels seem perfectly good quality for the price. I've put a lot of miles on them with no issues whatsoever.