I agree with posters discussing 1991. Here's the starting grid for Monza that year, together with what each driver would go on to achieve:
1. Ayrton Senna (3 F1 world titles, 41 wins, 80 podiums, 65 poles)
2. Nigel Mansell (1 F1 world title, 31 wins, 59 podiums 32 poles. 1 CART title, 5 wins.)
3. Gerhard Berger (10 F1 wins, 48 podiums, 12 poles.)
4. Riccardo Patrese (6 F1 wins, 37 podiums, 8 poles.)
5. Alain Prost (4 F1 world titles, 51 wins, 106 podiums, 33 poles.)
6. Jean Alesi (1 F1 win, 32 podiums, 2 poles.)
7. Michael Schumacher (7 F1 world titles, 91 wins, 155 podiums, 68 poles.)
8. Nelson Piquet (3 F1 world titles, 23 wins, 60 podiums, 24 poles.)
9. Roberto Moreno (1 F1 podium. 2 CART wins)
10. Pierluigi Martini (Le Mans 24hr winner)
11. Mark Blundell (3 F1 podiums. 3 CART wins. Le Mans 24hr winner)
12. Ivan Capelli (3 F1 podiums.)
13. Stefano Modena (2 F1 podiums.)
14. Andrea de Cesaris (5 F1 podiums, 1 pole.)
15. Satoru Nakajima
16. Emanuele Pirro (2 ALMS titles, 5 Le Mans 24hrs wins.)
17. Gianni Morbidelli (1 F1 podium.)
18. Mauricio Gugelmin (1 F1 podium, 1 CART win.)
19. Martin Brundle (9 F1 podiums, 1 World Sportscar Championship, Le Mans 24hr winner.)
20. JJ Lehto (1 F1 podium, Le Mans 24hr winner.)
21. Thierry Boutsen (3 F1 wins, 15 podiums, 1 pole.)
22. Erik Comas
23. Nicola Larini (1 F1 podium)
24. Erik Bernard (1 F1 podium)
25. Mika Hakkinen (2 F1 world titles, 20 wins, 51 podiums, 26 poles)
26. Olivier Grouillard
Six-time race winner Michele Alboreto and podium-finisher Aguri Suzuki didn't even qualify. But anyway, three drivers on the grid who didn't achieve significant success in a senior international racing series is pretty impressive. I don't think any of the grids of the previous years will be able to boast that.
The other thing I think we're missing is a driver of the Senna level. Alonso, Hamilton, Vettel et al are all outstanding talents, but I think that any one of Fangio, Clark, Senna and Schumacher would be the best driver on this grid if they had been of this era.