I don’t like the granularity either, really. And the problems with travel I mentioned in my original post on this idea.
The primary idea however, is to enable players, especially newer players, to engage in “limited risk activity”. So, not transitioning from “almost no risk” (high sec) into “Death Valley” (everywhere else).
The limit-by-security idea is to provide something that could be done with actually minimal changes or new mechanics - because CCP doesn’t really have a competent coding team. So gate limits and size restrictions are something we already have coded. It was also to provide a similar progression from “big ships” to “really big ships”.
Fewer/wider tiers could work. Ban Supers/Titans in low would have some effect, but would still give most players the “move from almost-safe to killer-deadly in one jump” barrier.
We could also have some new regions that could be jumped into that only allow say T1 frigates->cruisers. Use some of the lesser used systems. They just need to be accessible to especially newer players, but basically all players who simply want to dogfight in ships of size X without having to worry about getting ridiculously overmatched as soon as the first scout spots them.