If Story Points are relative and about effort, why not compare various projects sizes in SP?
First, I do not want to compare velocities of individual teams. All I am looking for is normalization of product size. To me, story points seem right for that, assuming that all teams get to see a common, reference story assigned with 1 SP. Team A might get it done in a day, team B might need twice as much, that is fine. But the total number of story points (were they working separately on a completely identical project), would be approximately the same, wouldn't it?
Additional point, I assume in projects with fixed scope and time, there is no point in estimating in SPs - you have e.g. 1000 MD to deliver 50 features, so whatever you estimate in SPs, in the end it would equal to 1000 MDs.