Apart from the subjective response to new visual stimuli, i.e. Mac-centric font smoothing in a Windows font blockiness environment, the other issues you mention can, for the time being, fall under that catch-all umbrella: "it's a beta".
NO, APplication stability is about only thing that can attributed to "beta".
System resource hog, apple's all apps have this problem, and they are not beta.
Security, there is no browser is absolutely safe, and apple's developer has been hiding behind the rock for 8 years, their ability of make secure windows app is questioned already, and its not a beta issue.
Non-native, can beta solve this? not likely
speed, webkit core/non-native are main causes, and apple can/will do nothing about it