Variations of this question have surfaced here from time to time. My two cents. In a race against time, all incremental advancements assist. Merckx would have done better in his hour record ride with more modern equipment, no doubt. The modern Tour riders have the TT specific bikes for a reason, they are faster but purpose specific. You touched about control, a different problem, note in mass start races TT bikes are not present, (rules aside, La Mond had the hybrid solution and that is now gone). Vintage bikes slower? yes, does it make a huge difference? No, not to the vintage bike enthusiast. I got great pleasure 12 years ago dropping the cat. 3 roadies on hills on a mtb. with slicks in training, now THAT was a psychological attack. If one can do this, smile at the same time for best effect.
Until the more recent advances, index shifting & differential brakes as an example, the evolution was very gradual. Weight is not that big an absolute factor, a perceived factor, YES, when I was racing my first races were on Clement Seta Extras (I was getting dropped), when I started winning, I rode 250's, later even heavier! Because the cost of not finishing was higher than the incremental advantage of light tires and rims.
On the track, I think that is a different matter, If I were to race again, my 30 year old track bike would fine save for modern wheels, especially as the nearest velodrome is indoors, for the serious races a disc rear wheel would be manditiory, with an aero section front. I would stick with toe straps (seen too many riders pull out lately), Outdoors, 30 year old equipment design is no problem, in sprint or mass start events.
Being very willing to ride a 5lb. heavier machine today if I could weigh as much as I did 20 years ago,
John Jorgensen
Palos Verdes Ca