PH> Can I check routing logic with you?

Yes the logic is to check if there is a direct address configured and route to them if so.  If there isn't a direct entry for that address, then it will look through and try to find the first routed match.

 PH> I know most routing tables work on the last rule that matches applies,
 PH> and clearly there's a defined direct route with 3/102 defined in 1/100
 PH> HUB .. but would there be a way to override that behavior to create a
 PH> forced rule to direct 3/102 netmail to 3/100 instead?

I just finished adding a "Bypass Direct" flag for echomail nodes which will disable direct routing for that node, causing it to fall back to the netmail routing policy.  Sounds like that should do exactly what you want!  Its in the latest prealpha for A47 as of today (my today (Jan 30), not the today of time travelers such as yourself).

Other "forks" of logic after that if you wanted them could be done by using the "NOT" function of the routing

--- Mystic BBS v1.12 A47 2021/01/29 (Windows/64)