It is arbitrary anyway you turn it. The belief in and worship of a supreme being (or multiple) would in my opinion be a good criterion to distinguish religion from philosophy but with accepting Buddhism as a religion that's no longer possible.
No loss whatsoever in that; "god" is both unhelpful and undefined at the best of circunstances. It is one of those words that are misused and abused far, far more often than not. I don't think that it was ever possible to tell a religion by its god-content, nor would it ever be advisable even if possible.
Judges who have to decide if an organisation has the rights that come with the label are struggling and come to different decision. Pastafarianism is a religion in New Zealand but not in Germany. In the US, religions that have the use of hallucinogenic substances as a ritual are treated arbitrarily. Native American use of peyote is OK, Rastafarianism is OK but trying to form a religion around LSD didn't the approval of the authorities.
There simply is no consistent definition of religion.
Indeed. And there is no good reason for any government to want to meddle in that difficult, inherently arbitrary art.
Such an attempt unavoidably would involve deciding to inhibit new religions to be while favoring whichever groups received recognition. Fertile grounds for restriction of religious freedom as well as abuse of political power.
Instead, groups should have the freedom to present their requests and have them granted or not on their own merits; being a "true" religion is immaterial for that purpose - and should be immaterial.