Gravel bikes — do we actually need them?

Gearing is what you put on it. Quite agree that 31/36 is not low enough to deal with severe riding, but a lot of 1 x 12 riders will have much lower and have easier options for switching front ring depending on conditions.

A couple of mph average is no big deal in terms of stats, but represents quite a bit difference in effort. Gravel bikes are much lighter and that mph difference represents physical effort.

I agree that MTB is more comfortable but it is a trade off and not all will agree on the balance

If you need front suspension, the conditions are too 'technical' for a gravel bike..

I think that is the difference, if you are riding technically, jumps and bumps, then that's MTBing, getting around off road keeping the wheels on the ground generally doesn't "need" suspension. Which bike is best may well depend on the mix, the cost of lugging a MTB around may outweigh the benefits, on the other hand there may be stuff on a route that a MTB can ride where a gravel rider might dismount for. Is dismounting a problem?

I swapped from MTB to gravel and the difference in climbing is fantastic.  Quite a bit lighter and no squashy front, even with the front sus locked.  With a lighter front it is also easier to pop the front wheel over a big root, step etc

Dismounting is no problem for maybe a rock step or rock garden however I've done some "gravel" events that had properly technical descents where you were basically on the brakes for a good few minutes. So I switched to a hardtail for those events and found them far more enjoyable. Just to be clear I'm not interested in setting a great Strava time just want to enjoy a ride over some mixed terrain.

And yet bike companies are building gravel forks and even fully suspended gravel bikes. So ok some of that is marketing to just get people to buy more stuff but I've also seen some gravel bikes at events where the owners are basically trying to replicate an MTB. I.e. 50 tooth rings out back with massively wide drop bars to keep some control on descents, even dropper posts. Absolutely agree that if all you ride are fire roads and tarmac, or you want to set a time in a course, then yes a gravel bike will be perfect. However, in my opinion and experience, a hardtail MTB will also work just fine for most riders and they'll have more fun and control when the going gets rough.

So they've recreated the drop bar MTB as used in the 1980s by eg Jacquie Phelan. Now it's called a gravel bike because, well, because segmentation sells. Look at the mountain bike, which used to be just a mountain bike, but now encompasses half a dozen sub-genres from downhill to trials. "Gravel" already covers a wide range, from nearly MTB to nearly cyclocross to nearly road touring, and has thrown up a number of sub-category names, such as "all road" and "adventure" but they don't seem to have yet crystallized into recognised categories. 

John Tomac's legendary use of drop bars for a downhill MTB race is worth a read.

https://roadbikeaction.com/throwback-thursday-drop-bars-on-the-kamikaze/

This.  
After a year on a Strael "All Road" I sold my 3 bikes - Ribble Carbon Endurance, the Strael, and MTB for a Ti Framed Gravel bike with all the DI2 trimmings and 2 sets of wheels.  

1x650b with Dynamo and 45mm tyres for Winter, Gravel and light MTB.

1x700c 48mm deep aero set for long roads and high summers 

Now I'm always riding my best bike. 

My good-bike is gravel with 40mm tyres. I ride with my road friends (lots of chat) and off road with others.  I love that it is a go anywhere machine certainly in Suffolk. The only think I change are the tyre pressures. When fitted with 2.3" tyres it is good for ridgeway or Dorset Dirt Dash.

absolutely, I think people mistake gravel bikes as somekind of MTB-lite offshoot, which is why they spend all their time trying to turn them into hard tail MTBs, when thats never been the point of them.

my gravel bike allows me to ride roads comfortably, the back roads which a road bike would take an absolute hammering on, and allows me to use bridle ways, woodland tracks that youd never remotely consider on a road bike.

but none of that requires an MTB, MTB suspension or even MTB tyres, infact an MTB would be horrendously slow in comparison.

Same here - my winter / wet weather / commute bike is a gravel bike but very much at the road end of the spectrum. 38 mm slicks, mudguards and 2x11 with easiest gear 34x32, so not even 1-1 and hence a bit wrong for gravel. It's probably most optimised for the commute due to the awful road surfaces, but does most miles on club rides. The only slight drawback compared to my summer bike is climbing needs more effort..

I would like to do more gravelly gravel, but removing the mudguards and changing tyres is a faff, and if I went all-in, I'd want a lower gear, so new cassette on spare wheels and possibly wrong chain length. Next cassette will be 34t at least.

Same here. Not many (any) "gravel" roads or "fire tracks" round here. I was looking for a bike that wasn't a "racing" bike for use on quiet roads and occasional tracks. I used to have what they called a touring bike, but they seemed to be thin on the ground, and eventually it dawned on me that "gravel" was exactly what I wanted. Took me a while to understand why they were called gravel!

I rarely ride off road (mostly MTB when visting my Dad) and the thing that I really noticed was that on the road if the bike is sliding around it is likely to get very "interesting" very soon, whereas off road a bit of sliding around is the default.

That exact thing freaked me out when I started on gravel a few years ago. Have got used to it now.

I'd quibble with that slightly.  Width is good but tubeless is a revelation due to the lower pressures you can run. 

Miller wrote:

... start riding on unmade surfaces. 

Or "roads" as they're known as around here.