Should it be either XX months probation or work with a company minimum 2 years before you can just be let go without reason not both?

It's really not, at least not in professional environments. In my experience probation failures are rare\* but sometimes mishires happen and you find that the person you brought on board doesn't have the skills they need, or isn't at the level they need to be. Probation is particularly valuable for more senior and management roles where it can be more difficult to adequately assess skills in the artificial environment of an interview. In general I would far rather weed people who aren't suitable out during the selection process, because it's pretty rough for someone to leave a job (that presumably was stable, even if they didn't like it), start with a new company, and then fail probation. Probation failure is really the last resort and, if it's happening frequently, it's generally a good idea to look at your hiring and selection processes to see if there are problems you can fix there to avoid hiring people who aren't well suited to their roles in the first place. *\*To give you an idea of what rare means, I've been in management and leadership roles off and on over the past 18 years, and out of all the people who've worked for me or who I've been involved in hiring, three have failed probation, and this number represents perhaps 2% of overall hires.*