Now compare this to side chains. With side chains you can compute in any given second EXACTLY has much BTC each side chain has allocated to it.
Yes but that has no direct relevance to how much
you can claim from the site chain "vault" if the side chain is flawed in some manner. Consider that.
If your point is that this has no direct harmful effect on bitcoin itself, I mostly agree (and disagree with cyperdoc) and consider side chains to be a bitcoin application that leads to more demand for bitcoin (to put in the "vault"), except for possible systemic and contagion effects, which are difficult or impossible to reason about in advance.