the Apex group is fairly similar to the SRAM Rival group, just heavier (Apex RD has a longer arm and can handle larger cassette cogs).
Rival is comparable to Shimano 105…so you are right about ultegra being about 2 levels higher. In my opinion, the reason Trek is offering the SC 7.0 with SRAM Apex group (and some really heavy Bontrager wheels) is just to get the absolute lowest price point for the SC 7 series…you know, to take on Cervelo for Tri Bike Supremecy. If you ask me, I think having the Apex group on a high end frame doesn’t make much sense. There are countless Slowtwitchers on here who are buying the 7.0 and upgrading the components, wheels, bars, etc. Essentially getting it just for the frame. But if they didn’t offer the 7.0 as it is, they would be eliminating a lot of potential buyers like yourself who would be opting for a P2.
I bet if anyone wanted to pick up an Apex group, there are plenty out there for a good price 