The short answer
Lightning wins on price (often $25k+ less for comparable trim), payload (~2,235 lbs vs R1T's ~1,760 lbs), Pro Power Onboard 9.6 kW (R1T has none equivalent at this scale), traditional truck format, and Ford dealer + parts ubiquity. R1T wins on range (up to 410 mi Max Pack vs Lightning ER 320 mi), off-road capability (quad-motor independent torque vectoring), gear tunnel storage, and adventure-focused design. Pick by use case — workhorse vs adventure rig.
Range
Lightning Standard Range: 240 mi. Lightning Extended Range: up to 320 mi. Rivian R1T: Standard Pack ~270 mi, Large Pack ~328 mi, Max Pack up to 410 mi (RWD), 380 mi (AWD). R1T Max Pack wins on range; Lightning ER is competitive with R1T Large Pack.
Power
Lightning ER: 580 hp / 775 lb-ft. R1T Quad-Motor: ~835 hp (Performance) up to 1,025 hp (Tri-Motor). R1T Dual-Motor: 533-665 hp depending on spec. R1T at top trims is more powerful; Lightning ER is plenty for a truck.
Payload and towing
Lightning ER: 2,235 lbs payload / up to 10,000 lbs tow (Max Trailer Tow Pkg). R1T: ~1,760 lbs payload / 11,000 lbs tow. R1T edges Lightning on max tow; Lightning edges R1T on payload. Both adequate for retail use.
Off-road
R1T Quad-Motor with independent torque vectoring at each wheel is genuinely best-in-class — handles rock crawling and adventure terrain at a level no other truck matches. Lightning has standard 4WD and electronic locking rear diff but is not built as an off-road specialist. R1T wins decisively for off-road.
Interior
R1T interior is more premium — Tesla-Apple-design philosophy, screens replace most controls, vegan leather standard. Lightning interior is more traditional truck — physical controls, large 15.5" portrait screen at top trims, leather available. Different design philosophies.
Price
Lightning Pro: starts mid $40s. Lightning XLT ER: ~$60k. Lightning Lariat ER: ~$70-75k. Lightning Platinum: ~$85k+. R1T Dual-Motor Standard: starts ~$71k. R1T Dual Performance Large: ~$80k+. R1T Quad-Motor Performance: $99k+. R1T Tri-Motor and Quad-Motor Max Pack push $120k+. Lightning is meaningfully cheaper at every comparable spec.