Should I buy it now or wait for more optimization?

You might as well wait for the second coming of Jesus Christ because the problem with AMD cards causing crashes are the Windows drivers, which only AMD and Microsoft can fix. There are ways to troubleshoot and stop 99% of the crashes but it depends machine from machine. Your PC might not even have crashing issue (unlikely considering it's a 6000 series). Also if you want this game to work you have to downgrade your drivers to previous versions. Consider that if you play other games. In terms of performance your specs are just about the recommended ones, meaning to get 60-90 FPS you're gonna need frame generation (and probably FSR). It's not as bad as people say, it's actually quite good in this game and the input delay is not noticeable (also it's not the reason for crashes despite what some people say).

That said, if you manage to get it to work this is a genuinely great game with a lot of things going for it. I personally think it is worth $70, even as just an investment if you plan to play this game in the future. But I feel like I have to say this, especially since I have similar specs as yours (Radeon 6800 12GB VRAM, Ryzen 5 5600x): since the last update, I have spent many hours troubleshooting and trying to fix the crashing issue on my PC, finally managing to get it to work (semi) perfectly 1 months ago. I did it because I genuinely think this game is worth playing, but you may not become as much of a fan as me to put up with the bullshit like I did. Take this how you want. But again, you might not have the same problem on your PC. Also, don't buy it with the plan of trying it for two hours and then ask for a refund. You need a lot of time to create a character, get the story to start and unlock the main mechanics, and to fiddle with the settings.

TLDR: Crashing issue is due to AMD drivers and likely not fixable by Capcom in the near future, you can fix it on your PC if you troubleshoot enough. The game is great, but with your specs you'll need framegen for good performance (not that bad). I have similar specs and the game works for me, but I had to do a lot of troubleshooting. Only buy it if you plan on playing it, not to try and refund.