The weight assigned to an LSP affects only the forwarding decision, not the routing decision. It does not change the selection of the set of ECMP tunnel next-hops of a prefix when more next-hops exist than the value of the router ecmp option. This selection continues to follow the algorithm used in the IGP shortcut feature.
After the set of tunnel next-hops is selected, the LSP weight is used to modulate the amount of packets forwarded over each next-hop.