I'm no expert but I've beaten the game many times on normal roguelike mode. I always put my stat points all into my two primarily needed stats (Strength and Magic in your case). Then, when I hit level 16, I start putting every point into Constitution until it's maxed. Then, I go back to building up the other 2. I'd bet the consensus says there's a better way to do it but it works for me. The HP helps.

Have you checked the ToME forum yet? There might be some tips/hints/clues/whatnots you could use to make your character stronger and/or survive longer. You don't even need to create a forum account just to read all the threads there. :)

You can find the link to the forum at the menu on the left or the top of this page.

Looking into game log usually helps a lot (you can see a little of it on character page you linked):

--Sharon The Peacebringer the level 22 ogre reaver was darkened to death by Faanfer the giant on >>>level 1 of Ambush!<<<.
If Ambush means you're attacked by patrol on world map - you should generally avoid those - they can sometimes get very hard as you'll be fightning multiple rare+ enemies.

--Sharon The Peacebringer killed Fagaga the human!
--Something hits Sharon The Peacebringer for (42 absorbed), 0 cold (0 total damage).
--Something hits Sharon The Peacebringer for (29 absorbed), 0 cold (0 total damage).
--Faanfer the giant hits Sharon The Peacebringer for (29 absorbed), 0 cold, (89 absorbed), 29 cold (29 total damage).
--Faanfer the giant hits Sharon The Peacebringer for 36 cold, 113 darkness (149 total damage).
The last visible message of your action in the log was you killing one of the rares. Then you're attacked 4 times before you got killed, by something invisible and anothere rare+ enemy. My guess is that you're slowed. Ideally, you'd like to fight dangerous enemies 1 by 1 whenever possible.

You should always have some cleansing inscriptions to remove detrimental status effects.
You had Curse of death on you which negates all healing you recieve. If you were using heals during this time you're wasting turns.
I suggest maxing Ruin pretty early - it's quite nice sustain. Bone Shield is also pretty good defensive sustain.

Heavy Armor is never wrong. you can argue when you have talents like trained reflexes (where you cant use it if you have anything heavier then leather in your Body slot) but even with it it is still debatable. With Mage Classes it is often better to go bulky and take the fatigue instead of being squishy with a Robe. also Reavers have access to Bone Shield so thats a huge defensive upgrade you should get asap. +Health on Items is the most important stats in the first 15-20 levels so you should look out for that too. And i dont know if you are aware of how Armor+Hardyness works but basically you should never exceed your Armor Hardiness with your Armor or it gets wasted. if you have 50% Hardiness it doesnt mean anything unless you have the coupled armor to go with it and having 100 armor but 0% hardiness is just 100 armor wasted. always have both on the same level. Also the game checks which armor you have equpped on the Body slot so you can have all your gear with heavy armor but if you have cloth equipped as a bodyslot it doesnt count as heavy and vice versa. keep that in mind.

There are quite a lot of guides or at least tips on the forums but most of them are outdated. There's a couple of threads on Reavers, you could take a look there.

If you're looking for basic info I can definitely recommend Cathbald's guide series: https://forums.te4.org/viewtopic.php?f=41&t=48659 (although the one on prodigies is outdated lol).

The thing that's really missing is like a basic guide on how to build a character, what stats and effects on gear are important early for different characters, prioritising early skilling etc. The details of this are too intricate to illustrate it all in a guide (too many classes) but I can definitely see a general guidelines for newbies being helpful!

I do suggest that if someone is writing a guide for a class but doesn't link to a winning character of theirs on Insane difficulty, don't take their advice. That sounds super elitist but there's just a lot of advice around which is either bad or simply wrong. (for example, Curse of Death only prevents regeneration, not all healing... much love <3)

Fundamentally, I understand the Reaver to be a rogue/mage assassin-type class, which is why you deal a lot of damage but can't really take hits well. The problem with this is, as you have noticed, TOME is a survival horror game and thus the ability to take unexpected hits is crucial. You do get bone shield but that's only good for taking the occasional stray hit, not for eating full frontal combos from bosses. Once they get past your shield it's a question of whether or not you can take the hits.

It may help you to think like an assassin: nerf your enemies with hexes, pinning, and spellshock before you close in and trade blows with them. Don't pick a fair fight with anything tougher than a normal or critter ranked mob.

If you're looking to balance the "glass cannon" class out, you can try going a tanky race, like dwarf or wight (my own addon, Playable Wight Race, adds wight as a tanky undead race option.) Unless you get a really broken race, though, thinking like an assassin, isolating and debuffing your prey will still be necessary. Always have multiple escapes in case stun puts one on cooldown or you're in a teleport locked vault. Always have an emergency heal or shield rune that costs 0% of a turn to use. Always have a plan.

Heavy armour is the normal way to equip a reaver since vim costs are not increased by fatigue. Your reaver may learn mana based skills (that would suffer fatigue penalties) like channel staff or premonition, but it is still a good idea to wear heavy armour since reavers should be in melee range most of the time.