Should 13th month be seen as a bonus or as AWS if its stated in an employment contract or company policy?

13 mth should be AWS but some company offer high salary without giving aws

Question doesn't even make sense. If it is already stated in the contract or company policy, then it will be what it stated there. Like other have already stated, 13th month is not compulsory by company. So if your company got give, then it is good.

I always felt that the 13th month bonus is under AWS. Because if you divide 52 weeks by 4, you actually get 13. So every month, you actually only get paid to do 4 weeks of work, then those extra days every month add up to a whole extra 13th month which you get paid for if you stayed the whole year in the same company.

I would prefer it to be under AWS rather than bonus.