Annie,
Anytime you choose lenses with large apertures like f2.8 on the Canon and f1.8 on the Siggy you are talking weight. No way around it. Fortunately for a landscape photographer large apertures are not required or even desired. As for general purpose these are two of the best lenses made anywhere.
"I would not recommend the Sigma 18-35mm simply because DPP cannot perform lens correction on it."
This has to be the most ridiculous reason for not getting the best lens for your needs. Because you can't use a free editor.
"The 50 mm F/1.8 ssounds like a great idea!"
It's not. 
50mm on a cropper is not a friendly focal length. Add to the fact you can't zoom it and it is not a lens I would ever recommend for a hiker or landscape photographer. It is a specialized purpose lens. It make a wonderful second lens.
It seems weight is still is your main most concern. Balancing that and what you want to do the T8i and the standard kit EF-S 18-55mm is STM lens is probably your best go. Later on if you feel you need an ultra fast lens do check out the Sigma 18-35mm f/1.8 DC HSM Art Lens.
One other thing check out the Black Rapid strap. It will make the weight of camera gear disappear.
I use them on all my 1 series with very heavy lenses on them. Sometimes two at a time!
@amatula15 wrote:Thank you, everyone!
I purchased a used Sigma 17-50 F/2.8 during lunch. I can return it if I don't like it -- will check it out tomorrow. I did love the weight (the store also had a Canon 18-55 F/2.8 too)
The T8i does have HDR filters and some level of customization. I believe it was the replacement for the 77D.
Thank you, again, everyone. Now I just have to see if the 90D is too heavy...
Annie
Yes, the T8i may have in-camera HDR. It probably requires that you shoot JPEG, and it probably does not save the original files. Most of the time, you want to process HDR images in post, but I do not think that feature has been added to DPP, yet.
But, I mentioned how Rebels lack many features that photographers find to be highly desireable. HDR is probably not in anyone's top 5 because most people prefer to process the images in post. One key feature that Rebels lack is weather sealing.
The 90D seems able to survive getting wet, although I would never let it get quite that wet. If one of your primary use cases, are taking hikes and capturing landscape photos, then you will want a camera with a more rugged body than a Rebel series.
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I like to hike in the woods, too, although not very long hikes. I use a Black Rapid Sport camera strap when I am walking about on level ground. It is not comfortable to wear when you are hiking in woods. Besides, the camera is open to being bumped and banged.
I use a Lowepro Toploader Holster when I am hiking in the woods. Often times i use the holster when I am wandering around on level ground at an event, because it "hides" the camera. The Black Rapid Strap is great to use when you need your camera in your hands "right now." Iuse it most often when shooting sports, or at an indoor social event.
If you're taking long hikes, then you want gear that does not need to be pampered. This goes for both your camera body and your lens. I would advise either the 80D, or preferably the 90D. The T8i may be great in the backyard, but it may be a little too fragile for long hikes, which almost always involves some sort of climbing up and down hills, and going through brush.
"Yes, weather proofing does sound better,..."
Weather sealing is as easy and cheap as a zip plastic bag and a rubber band.
You are placing too much attention to post editing than you need to. Most of it now is totally automated. Upon import from the camera, presets will handle lens correction and apply your selected in camera setting and add your copyright. All as you sip a nice mocha latte. Weight still seems your main most important issue. One last thing don't believe all you read on the ole inner web about the 90D or any gear for that matter.
