Unfortunately, it seems like both the controller and file system are brain-dead on the RPi.
Namely, you have a cache that detects this sort of (relatively-common) append-only operation, and buffers it until it makes sense to actually write it (either because the disk is otherwise unoccupied or because you are close to the limits of your power buffer).
Alternatively, you have a file system that actually knows the advantages and limitations of flash. You can do append-only files efficiently on flash (without doing all of the read + write dance). "All" you need to do is take advantage of a bit of scratch space and knowing how flash works. Namely that you don't necessarily need to flash a block to write to it, as long as you are only turning zeros to ones (or vice versa, depending on how physical bits are mapped to logical bits. Multilevel flash is a little more complex, but still doable). (For instance, instead of having one filestamp, you have space for 16 filestamps, with two bytes at the beginning, all initially set to all zeros. You check the last bit set and use that filestamp. Congratulations, you now can update the file 16 times before needing to reflash the block. If that's not enough, you can extend it arbitrarily (note that you can do this dynamically for files only when they are updated enough to warrant it!) And metadata/etc can be done in the same way. For something like a log file, you have, say, 16 slots for how much of the block is occupied, and a pointer to the next block (or null). You append the content of the new log line to the file and add the new content. One write, no blocks being flashed. (Two writes if/when you run out of space in the block.)
See, for instance, https://github.com/bnahill/FLogFS/ or https://en.wikipedia.org/wiki/F2FS/