Default config file

This is a personally biased opinion so take it with a grain of salt.

I don't think that reducing game defaults any lower would make sense since they're already low (default) and based on a 10 years old game that's considered ancient in technology era. Specs you mentioned are severely outdated. I mean by utilizing hardware you do, game specs are the least of your problems - there's OS resources, security as well as other factors that create challenge before you even come to application layer. Additionally, if some logically common sense is used, than it's the general rule - the needs of many outweigh the needs of few. By lowering specs by default and offering bunch of settings to users that generally feel uncomfortable with regular settings let alone any more specific stuff will mean, that most of users will end up utilizing half or barely any resources simply because they wont want to change it, even although their computers would easily cope with what a 10 years old game has to throw at them.

Personally I'm always leaning towards some kinda of middle ground but in this case, it doesn't make sense. I think better approach would be to simply add a single setting in menu that would execute a pre-defined config if user desires so. It would boot with default (current settings) and offer low & high specs options, where low would downgrade some commonly used stuff like you mention to some lower (safe) levels, with picmip 2, zone and hunk usage lower etc..while max would naturally do the opposite and boost stuff to some (safe) max levels. That would be a solution I think it would work best, naturally it would still at times fall down to user's specific needs, as you simply can't put all the cvars in a config that will make everyone happy as needs vary but most of basic stuff could be utilized like that and wouldn't interfere with what majority has set now.

That's my input on it.

While I agree that maybe not all settings are optimal but you'll have to run a custom config to customize the settings to your needs, you're probably one of the very few who run it on old hardware

about other games: no interest rtcw is the only game I love and played

Yes and no. Game had support for voodoo, riva tnt and even ati rageII etc..but that doesn't mean it was ever meant to run at high settings (for those times). By the time game came out, only but few people could actually hold stable 125 fps with graphic max'ed out.  Now days, most of people can easily hold 333 without a second thought. So it all depends from a perspective which in today's era and way of things means that low supported hardware from that time is now considered severely outdated. 

I do agree there's no reason to stop supporting old hardware if it's still possible, but I tend to disagree that everyone should be treated as such, if anything quite the opposite.

As for rate - ping is a relative thing. In certain situations you can with combining various tweaks even get 0 ping but that doesn't mean it's actually the case, in mp world that's known as unhit tweaks. As for your question, now days any decent dedicated box can easily handle 20000 or 25000 rate, and that makes game smoother for client as stuff is where it was suppose to be. Low rate is usually a thing with home hosted servers where owner doesn't have a 100mb+ connection and/or cable fiber. Although, in this particular case where most of coop servers are in fact home servers, rate could be set to 10000 but that's arguable as well.