I think the multi-device strategy is a clear winner. The lifetime value of a console itself is probably not terribly high. After all, most game companies do not sell hardware at all and a few who have eventually gave up (Sega, Atari).
Plus, the PC, Switch, and iPad markets are largely orthogonal to the XB/PS ones. Content for the former probably doesn't compete with the latter, so it makes sense to sell in those markets. And lastly, could you imagine how Sony execs would feel if their best selling PS titles all came from MS studios? That would certainly put them in an awkward position to suddenly be financially dependent to some degree on MS.
