Perhaps not what you want to hear, but multi value fields and lookup fields in tables are to be avoided whenever possible. The problems they introduce are usually not worth it -
or so you're beginning to realize. A properly normalized set of tables is preferred. BTW, Tag is a specific property and multi-value has a specific meaning. If I've misinterpreted your post that would be why. For example, there really is no such thing as a list of tags.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.