Subaru and Mazda are fairly small so I wouldn't expect a lot of R&D from them. Toyota has been really successful with hybrid which to me, seem like the best solution until EV range cost, and infrastructure improve.
Mazda engine R&D is seemingly quite impressive: the SkyActive X engine is an unusual ICE gasoline engine that takes ideas from diesel, with greater fuel efficiency and horsepower.
Those two are weird; they use to have a lot of out-there designs (boxers & rotaries respectively) but seem to have slowed down on the innovation since then.
Not much similar. Mazda is known for new engine architecture since 2010s. Subaru is known for stucked at boxer architecture.