With a recent patch, a few months ago, you brought higher rank basic runes (rank 4-7) into the droptable of mobs.
In my opinion, this corresponds well, to the higher level mobs, and may have been forgotten by the original developers, so good to have this.
But, what was the plan behind this ? Do you plan any changes ? Currently these runes just make more items in the bagpack.
So, my suggesttion is, change the requirements to upgrade runes up to rank 10.
In the current state, you need 5 runes to upgrade to the next rank. This leads to a massive amount of runes, if trying to get from low levels to rank 10, not even talking further.
Back in the days, it was a fun and interesting part of the game to build runes from the base runes.
My suggesttion is:
Up to rank 10, change the requirements to only 2:1 ratio instead of a 5:1 ratio.
This may encorage people to build runes at a least reasonable way/cost and build better runes from there, spending transmute charges, and using these runes instead of trashing them on loot.
Additional (bonus) suggestion:
If a rune was build (and not bought from IS), remove the max rank limit. So, if people want, they can craft/transmute/build runes higher than rank 13.
I would understand your reasons, why it is not allowed for IS runes. but with built runes, the situation will be different, as the amount of runes is limited to drops, and still require a lot of base runes.