for example, consider that getting stats to 50 practically requires them to start at 40, (even with both aptitudes its gonna be a fairly long campaign for you to buy +20 in any stat) and even a stat of 50 (impressive by guard standards) is still only a 50% pass rate. for things like agility, which you use to dodge which is realistically the only way to survive in this game short of impressive cover a 50% pass rate really isnt that optimistic
"Impressive by guard standards"? The guidelines, at least in Dark Heresy, is that a 50% in a characteristic is "heroic" level. 30 is average (and not for a malnutritioned, close minded hive worlder, but a healthy, intelligent individual),35+ is above average, 40 is "impressive", and 45 is really high for a normal human.
Now, as you say, it still entails a 50% fail rate. However, 1) skills should only be rolled when something is actually challenging (or when timing is an issue) and in most "easy" cases with a bonus. 2) Skills can get upgrades. You can get up to +30 with a skill. Even with a stat of 30 that is a 60% pass rate before you even consider modifiers for difficulty (which genuinely hard things aside should usually be at a bonus). Dodging on 80s for someone who has 3 levels of training 3) In combat and opposed checks the actual level doesn't matter, it is the relative level that matters. If two people are opposed the person who has a 50+ is much better off than 30, as they are more likely to pass, and if they pass they are more likely to pass with a bigger margin. If they fail they are more likely to fail by a smaller margin. Combat is similar, but not exactly the same, but as the base difficulty to hit is so low, dodge just represents the final line of defence. Now, this is slightly off set by the fact that it is relatively easy to some positive modifiers to shooting, but even 30% dodge is not irrelevant, especially considering an average guy has only got a 50-60% to hit you even with positive modifiers. Throw in some cover (meaning some hits get turned into harmless hits on cover) and you are actually not badly off.