head to head
vs
Grid 2vsIndy 500
Grid 2 leans Execution (Practiced Mastery); Indy 500 leans Execution (Pure Mechanics).
Grid 2Indy 500
Axis by axis
Execution7 vs 6
Grid 2 leans harder on execution: Car control through corners is the entire moment-to-moment test
Reads2 vs 3
Indy 500 leans harder on reads: Head-to-head races reward anticipating the rival's line
Variance1 vs 1
Even - both lean on variance about the same.
Optimization5 vs 3
Grid 2 leans harder on optimization: Racing lines, braking points and car selection are studyable
Two games can score the same on an axis and still test it in very different ways - read each rationale, not just the number.