As one who flies the route at least once a month on business rest assured the flights are normally pretty full and rarely cancel, I am lucky if I book a week out, many companies have contracts with the airlines so no advanced booking isn’t the same financial hit it would be to an individual, yes if you don’t buy seats you will most likely end up in the middle section, all airlines that fly the route have positives and negatives but ba does a decent job and in the end the differences are more about preferences than anything else