In checking DL.com it shows the flight from SJC landed early this AM, and the flight to PHL was boarding, so it is safe to assume it would land in PHL near the scheduled time.
This is a prime example of why DL does not let you change flight plans for free just because it is raining in ATL (or any airport for weather)
There could have been other potential problems of the other flight not make it to PHL on time also, MX, sick crew member, etc.
While being pro-active sounds good my experience shows it rarely works.
An example last spring:
Miss connected in ATL (weather) to IAH on Sunday PM DL could only confirm a seat on Tue AM.
I stood by on the first flight to IAH, did not clear.
I took DL to PSN on DL then to switched to CO to IAH. Sounds like a good plan?
When I got off the DL found out CO canceled. They put me on a taxi to MOB, then took an extra section to IAH. Arrived IAH about noon.
Was all the changes worth it? I am not sure. As a DM could Have I cleared on the next flight to IAH or HOU? maybe.
The long and short of it, in my experience I have found it better to stick with the original plan, no matter how bad because Murphy's law is in full swing that day.