Sizing was deregulated in the 1980s, and I don't think we can put the genie back in the bottle following the (industry avowed) vanity sizing of the 1990s, much as I wish it could be done.
What I'd like to see instead (because I think it's more achievable) is
a) sizing always accompanied by a chart that gives measurements in cm & in, and for those the be "true" measures, not allowing for people who pull the tape measure in tight (annoying when you're drowning in excess fabric, having ordered a 29" waist and it measuring 32)
b) a change in rhetoric, so that people no longer think of 12 as "medium" as that maps to the 1980s, since then, everything has changed (by vanity, not the old-style revalorisation) and we need to start thinking of 8-10 as normal/medium, 12-14 as large, and 16 and above as the XL sizes.
We live in an obesogenic society, and the population is much fatter than it was. As you can see from my suggestion, I want peoples perception of clothing sizes to reflect that a lot off the population is fat. It could be done differently, by revalorising so that 12 is indeed "medium" again. But that cannot mean the same thing as an 80s 12, where it reflected a healthy weight.
On current sizing, it's possible to be obese but wear 12/14 clothes comfortably. Which is of course fine, provided the perception of those sizes is indeed "large, but that's typical now" rather than "medium, which means normal weight")
Size of course would not matter if obesity did not cost the NHS so much - it's implicated in so very many conditions, and the damage creeps in over the years of being fat - people can feel fine and vigorous for many years whilst the silent damage is being done. Especially if they think that wearing a 12 means they're OK.