> there is some researching showing that fructose can be harmful but the glucose/fructose content of HFCS isn't significantly different from sucrose

Indeed a lot of people ignore this. Still it is worth pointing out that

a) a higher glucose content due to sucrose based sweetness helps absorbing fructose in a home-made cake.

b) the ultra-processed cake likely got added a fair share of sugar alcohols (keeping it moist) which for a single digit percentage but still significant portion of the population interferes with fructose absorption leading to fermentation in the gut.

c) the longer and cold storage of the industrial cake will lead to an increase of recombined starch which is harder to digest.

(a, b due to fructose transport from gut less efficient than for glucose and the transport part relying on presence of glucose. Some people suffer from fructose mal-absorption where the main transport mechanism is not working and the backup mechanism can be blocked by sugar alcohols)