Here is excellent engineering perspective on torque variation vs. crankshaft angular position. In 4, 6, 8, 12 cyl engines. Current F1 engine probably best represented by the chart for "odd-fire V-6"--
http://www.epi-eng.com/piston_engine_te ... ngines.htm
An even-fire 6-cyl engine still has moments of negative torque (rotational deceleration). You have to go to ~ 8 cyls to maintain positive torque all the time. A heavy flywheel on a 6-cyl would reduce the severity of its peaks vs. valleys, but it would not prevent the negative-torque valleys from existing.
Conventional wisdom is that engines produce more steady-state power with a heavy flywheel, and this is due to crank vibration modes messing up timing and other issues. F1 engine people understand the torsional vibrations quite well, plus now they monitor individual cylinder pressures (!!) as the crank turns, so by sensor/computational brute-force they eliminate power advantage of flywheels. If clutches and spec-dimension gearsets can handle the torque fluctuation with no flywheel, then I guess no reason to have one?