The $3,100 is not the variable doing the most work here. The assumption carrying the most weight in your post is that professional content should have compressed days-on-market or held your price against a soft Q4 market in San Marcos. Content does not do either of those things reliably. What content does is reduce friction at the decision point for a qualified prospect who is already in range on price. If demand was thin in that submarket in Q3/Q4, you had fewer prospects to convert, and better photography does not manufacture demand that isn't there.
The $150 under ask after 94 days points toward a pricing problem, a demand problem, or both. Either you were priced above where the market cleared in that period, or the prospect pool was shallow enough that you ran out of time and took what came. A soft Q4 in a secondary Texas market is a credible explanation for both. You would need to look at comparable vacancy rates and achieved rents for similar fourplex units in San Marcos during that window to separate the market problem from a pricing error.
The risk you did not mention is that $3,100 for a content package on a two-unit vacancy is a meaningful cost relative to what you lost. At $1,295 per unit, two units vacant for 94 days is roughly $8,100 in lost gross rent. The content spend was about 38% of that loss. That ratio matters when you are deciding whether to run the same playbook on the next vacancy or reallocate toward a pricing adjustment or a different leasing channel.
The real diagnostic question is what the comparable achieved rents were for similar units in that submarket during the same period. That number would tell you whether $1,295 was a market outcome or a concession you could have avoided with different pricing earlier.
What was your pricing strategy going in, and did you adjust before day 94 or hold the ask the whole time?