certain beliefs are simply products of their time, I suppose.

This is definitely important to keep in mind. Even though the Buddhist texts and ideas were far beyond their own time, they were not totally immune to some of the biases of their own time.

Something I haven't seen anybody mention in this thread is that gender/sex is fundamentally irrelevant when it comes to spiritual beings. Technically speaking, in Buddhism, nobody is a man or a woman, only their body is such. In the higher realms, many of the Devas and other such beings do not even have any sort of gender or sex traits. For the most part, I would think any of the Buddhist ideas about gender related more to the actual process of taking up a monastic life in that given time period. From a meditation/technical perspective, women are perfectly capable of achieving all of the same meditative states and aspects of attainment that men are.

is Buddhism more relaxed when it comes to scriptures and traditions being changed to match updated cultural attitudes and beliefs?

Depends what you mean. At the core, much of the essential teachings in Buddhism do not have much to do with ethics or philosophy, but rather, mechanics. Enlightenment, in rough terms, is about transforming the mind and purifying the mind, to conquer karma and other impermanent mind phenomena, to escape their influence over rebirth. These things can never change from culture to culture because they are not made up rules, but descriptions based on the mechanics of the mind/universe.

For instance, while the Buddha may say killing is wrong, and thus advise against doing it, he'd also argue that killing is an action that will almost always generate negative karma, and thus negative influence the direction of an individuals rebirth. Some argue there are a few circumstances where it would be okay (such as the other person desiring/asking for it, and then obliging without any malicious intent).

It is however worth keeping in mind that the Buddha did set rules for monks in his sangha which were not explicitly necessary to achieve enlightenment, but moreso served to help prevent his monks from doing things that would inhibit their progress.