Its a deliberate feature of the combat. Alongside Strength = Attack Power = Health, it forces the player to engage the turn based combat differently than the average turn based game. Its annoying when you underestimate your enemies, but it can also be used to your benefit. At the start of most battles, your characters get to act more often even though both sides have the same amount of turns. When you start to out number your enemy the situation flips. I found this a refreshing change of pace within the genre. You can play the game on higher difficulty and it is makes it less easy to overpower your enemies and lose your turn rate advantage. Easy mode is less easy than it first seems because killing is much easier, but giving a strong enemy turn rate advantage on easy is still quite dangerous.

By the way, most abilities/stats when upgraded do make the characters better in very straight forward ways. Your main concerns when upgrading a character is the tradeoff of passing up better upgrades or using your renown for food/items. Too much strength though can put you in a jam. Kill this enemy and increase the turn rate of his comrades, leave this enemy healthy and he could do some serious damage on his turn. The heart of the combat is to time your movement/attacks to prevent dangerous attacks on your party while crippling the enemy side. Timing your kills is an important tactical choice with more nuance than is typical for the genre. Some enemies are dangerous even with low strength. Some times killing an enemy is an important positional decision. Even dragging out a fight against 1 Strength grunts can weaken to party too much for back to back battles. When you get all your kills after maiming the whole opposing side, you waste the willpower gains from kills. All of this and more creates layers to the strategy.

Also I'm bias here, but upgrading the early game hero (Gunnulf) that does 14 AOE to 3 enemies surrounding him is something I don't recommend doing at all. That guy is overrated by people who upgraded him quickly. Pound for pound he is the worst hero at rank 1 & 2 (he can be salvaged with a lot of upgrades). If you do buy this game and only want to beat it once, don't upgrade him at all. There are much better characters and they come with the added bonus of being harder to screw up. Hakon / Mogr / Yrsa >>> Gunnulf. The fact that he can have the highest strength in the game is not useful at all on normal or easy. On hard, the high strength Gunnulf build can be useful, but is by no means needed. Also he is one of the worst characters for the final boss fight, his ability is completely useless in the battle. Not worth even one rank up in my opinion.

As a veteran of the game i agree completely with the previous commenter on how the combat flows, and regarding the layers of tradeoff in timing your attacks as maims or kills.

If you have any experience with the RPG or tactical game genres then you may be familiar with the "win-more" phenomena where, for example, if you can a;ready kill the bad guy in one hit, then getting more Str is an inefficient investment when there are other areas to improve. In this game maiming (taking enough str from an enemy that they are a non-threat) an enemy can be more valuable than killing them so the "win-more" dilemma can be doubly important.

As to whether you should get the title or not, I will say this game is one of the most challenging and satisfying games to play of all the strategy RPG's ive tried and it is also very unique and the story is beautifully told.

As a brief address to the Gunnulf tangent I do think that for newer players advising them not to "all in" on Gunnulf is very good bc at normal and medium difficulties too much str takes away the ability to not kill and his unit overall has lower stats than other units if you look at their potential maximums. However specifically for Gunnulf +1 lvl to get him an exert and 1 more armor will help him massively by improving his mobility and the first level up is only 5 renown. Positioning is everything in this game and a lvl 2 Gunnulf can set up multiple easy kills for other characters for a comparatively minor renown investment.

No, they never address the combat's problems, unfortunately. A mix of stubbornness and diehard fans coping that a plainly terrible system is 'very good, actually! in fact maybe the best system ever made!'

I don't usually mind challenging combat systems that demand out of the box thinking but the combat in Banner Saga feels very arbitrary and too counterintuitive to me. A system where taking down an enemy can screw you completely, without even giving you the option to aim for wound instead of kill, reeks of design flaw.
It feels more like a puzzle game, but in that genre arbitrary rules do not usually hurt the immersion.