This has already been discussed at length and your proposed solution is too complicated, especially since Yache Berry is not the only reason why Garchomp is broken. I'm not going to summarize the countless debates that have been had over this. If you want to read them, you can search in Stark Mountain and/or Policy Review. Suspect testing is the current method of determining tiers, is relatively simple, and will remain so for a while.
Soul Dew is strictly different, because Latias and Latios are the only things which can use Soul Dew. Therefore, Soul Dew is banned completely from Standard. Other Pokemon are able to use Yache Berry.