Alatar, I see where you are coming from in drawing your parallels with Shards, but I feel like what we're seeing with Splinters may be some of what BS has said about there being things in each realm only shadowed in the other realms. As such, then we do see some Physical and Cognitive manifestations of Splinters, but they would still be primarily Spiritual if my theory holds. I also really like your idea of Splinters being able to link into people's spiritwebs, which I would love to take as evidence for shardblades possibly being Splinters given that BS has described it as such in questions about stealing shardblades with Hemalurgy.