Rear tyre wear

You're getting 3000 - 4000 miles out of a tyre, some of which is on gravel. That's not bad wear, performance or not. 

I also like the Hucthinson Sector 32. I did 4000 miles on the rear (I'm 82kg) and it still felt like there was a fair bit of tread left (i only replaced it because it had a couple of plugged punctures that were starting to fail). I was under the impression that the Overide 35 was almost the same as the Sector but with more knobbly shoulders, so I'm surprised to see how worn yours is. 

Big fan of the Hutchinson Sector in 32c. Totally useless once those bridleways get wet though.

Have you had a look at Clement (now Donnelly) tyres? I'm getting good wear from a set of MXP 33c. My version aren't officially tubeless but that's how I'm running them. The X'PLOR MSO comes in tubeless ready and gets very good reviews as a adeventure/gravel tyre.

Ps. Which did you rate higher? Speed, grip, comfort, punctures?

I was about to put one of these tyres on my gravel/commuting bike. Based on your experience I will get about 3000 miles - is that right? Slightly different to the marathons currently on there- done more miles than that and no sign of any wear!

I am on my second set of Schwalbe S-Ones (pre-cursor to the G-One Speed) and mostly use them in winter for road riding and commuting, with the occasional trundle on gravel roads. I too have found that the rear wears pretty quickly and exactly as your picture. I would concur that although it is a little frustrating, I would not expect much better from such a relatively light weight ‘performance’ tyre. My opinion is that knobbly tyres like these will wear quicker when used mostly on tarmac, as the high spots (knobs) mean that the load is not spread across the whole tread like it would be when used on gravel/dirt. Also your back tyre is doing the extra work of providing traction for propulsion so is always going to wear out much quicker than the front. I tend to always swap my tyres front to back once the rear is starting to show signs of a worn strip down the middle to try and extend their useful life.

Schwalbe themselves market the G One as a high performance tyre with a relatively short lifespan:

https://www.schwalbe.com/en/offroad-reader/schwalbe-g-one-speed.html

If you're willing to have a 32mm tyre then the Hutchinson Sector 32 could be worth a shout, I use the Sector 28 and it looks like new despite doing around a thousand km's.

As the others have said the more gravel you do the quicker your tyres will degrade.

I'm of the mind though that I'd rather have good performance tyres and just accept they will need replacing more often than tougher, slower ones.

Don't forget that anything with a tread will wear quicker than a fat slick tread. Gravel also is hard on tyres not easier. Throw in the fact that your tyres have been fairly light by some standards and the wear isn't suprising.  As gravel needs no tread anyway just use some hefty road/touring/hybrid tyres.

That's reasonable wear for a performance tyre. if you want longevity, try Schwalbe tour range, much longer life
https://www.schwalbe.com/en-GB/tour.html