If your thesis is "UBI will be insufficient to get us where we want to be, we will need to make other changes" then at that vague level I can't really object - I certainly don't imagine UBI will fix everything forever.
But I don't think the improvement is temporary in the sense you mean. There are limits to how much UBI can inject at the lower end of the economy, but there are also limits to how much can be "siphoned away" - a raise to the cost of a good or service increases money saved by finding alternatives, some of which may be offered locally. Consider rent as a common example - even in the (extreme, unrealistic) case where all lodging is is owned by a single person and no new housing can be built, raising the rents demanded increases the benefit of cohabitation, enticing more people to do so.
But I don't think the improvement is temporary in the sense you mean. There are limits to how much UBI can inject at the lower end of the economy, but there are also limits to how much can be "siphoned away" - a raise to the cost of a good or service increases money saved by finding alternatives, some of which may be offered locally. Consider rent as a common example - even in the (extreme, unrealistic) case where all lodging is is owned by a single person and no new housing can be built, raising the rents demanded increases the benefit of cohabitation, enticing more people to do so.