A good definition of marriage is that it allows people to share rights which is why it makes investing together or having kids a lot easier. But it also makes things a lot more stable in other ways, it means there's always going to be someone to make medical choices for you, and there's going to be someone you can trust if you ever have a legal problem, etc.

Marriage really isn't for the couple, it's for society. Having stable families (whether they involve kids or not) is good for everyone, so the government gives people who make some kind of commitment to each other some benefits that make things more stable for them. And in places like the US they also usually make it cheaper via taxes.

I know lots of people who have made a commitment to each other and haven't gotten married and have been together for decades. The commitment is what's good for the couple, and a lot of times it makes sense to get married at the same time, but that's certainly not a requirement. And your two main arguments are against making a commitment to someone.

And maybe there is something to your points, you listed two of the biggest negatives to getting married. But you listed zero of the positives, is that because you don't think there are any positives at all? If you're going to make an argument that something isn't "worth it" you can't just list the negatives because that's only half the comparison.

It's like saying "this refrigerator isn't worth it because it costs $300 and $300 is something I could spend on something else." Yes it has a cost, but that's not all it has, it also has benefits you get for paying that cost. A compelling argument against marriage should list the pros and cons and show why the cons clearly out weight the pros.