Looking at the numbers the healing from the signet’s passive seems to be inline with our other heals. Using the signet’s passive over the active of another heal is trading the secondary effect for the convience of not having to spend that second every so often casting your heal skill. That seems like a fair trade to me.
The real problem with the signet is that its active is weak in just about every way. Even the trading of healing now instead of over time does not work because of the cast time and how small the heal is.
To make it a button that it is ever worth pressing it needs to be buffed, either by making it a stronger heal, or by giving it a secondary effect that it is worth trading overall healing for.