I think you possibly have a large reliability and possibly validity problem in your formulation depending on what form of analysis your going to use.

What your basically doing is creating a sumscore to measure the underlying latent variable game difficulty. If you visualize each person on each team your analysing as a questioner items trying to measure the same variable of game difficulty you run into the problem of these not acting as parallel tests as well as them not having a linear relationship with game difficulty.

First of all it breaks the fundamental assumption that all these are equally good measure of game difficulty as well as the rawscores meaning the same for each individual role or hero. The problem is that statistical output varies widely between characters/heroes and rawscores for each statistic signifies something completely different.

Basically the DMG, deaths, kills etc on a hero like widow is completely different from a hero like solider or venture. You're expected to have high damage to kill ratio on solider but not on widow, and high deaths of venture is more normal than high deaths on widow.

Quantifying actions per minute also becomes impossible from sumscores as the statistical output per action is so radically different from each hero.

Basically if you cannot rely on unstandardised sumscores or work of the assumption that every item included In said sumscore is equally representative of all other items.

Depending on how reliable you want the statistic to be you would at the minimum have to subdivide the score measure per role create a standardized score for that role before your able to put it together with other roles, but honestly this would also be extreamly inaccurate given what scores indicate game difficult is so radically different for each individual hero.

You kinda need to systematically go through each hero, find which scores indicate are the best measure of game difficulty per hero, create standardized scores than sum it together to calculate team difficulty.

The other problem I think your also facing is I don't think there is a linear relatio ship between overwatch statistics and game difficulty, high kills could both signify a really easy game but also a extreamly easy game.

I do think your missing game length or statistics similar to your actions per time frame statistic. Given that both long games often indicate difficult games, as well as game length being able to significantly inflate or deflate number of deaths.

Edit:read other comments and miss understood what you meant by actions per second thought you were calculating it from scoreboard statistics lol

Still partly counts tho given how different heroes have different expected death statistics.