Pressure suits like the Fox Flak, Dainese, Alpinestar or several others, are probably the best protection you can get ... yet still have enough air flow to survive.
But always alternatives for heat. I would NOT ride without sleeves unless you add Elbow guards. Lots of crashes involve forearms, hands and elbows. Protect them.
For years I rode dirt bikes with ONLY elbow guards and gloves up top and my Camel back as my
back protector. (better than you might think!) Of course I wore knee and hip pads too. But no chest or back protector.
I raced this way. Not smart really, but it can be done. (TIP: Don't crash too hard!)
In high heat/humidity full mesh is the go ... but no full mesh gear offers the protection of the Fox (or other) pressure suit. The problem is packing it when it gets cold and you must revert to your "other" riding jacket.
You "could" just use the pressure suit only and add layers over it. Like a light enduro rain jacket with a few layers of Merino wool sweaters? Might work?
So many approaches here. So much depends on weather.
Once place I found I was not happy wearing a pressure suit was in very tough, slow going on single track trail. Too hot. But I'm out of shape, overweight.
If one were in good shape, well hydrated and strong ... then you really can't beat Ride Far's set up for REAL protection. The beauty of the pressure suite is how the armor is held tight to your body. So when you crash it's where it should be to protect you. Built in Padding in jackets and pants can never do this properly.
I wear mesh dirt bike pants with Dirt bike style knee guards. ONly way to go.
Also, padded shorts to protect hips, tail bone, thighs. These ARE HOT and get really really nasty if you don't wash them everyday. A problem for me.
If you can keep moving, even 20 MPH, you'll get enough air flow to stay a bit cooler.