Thank you!
Aaagh! Now I need to buy!
(Thanks for the tip!)
Really, Epic was a bit more realistic in that Space Marines were meant to work as allied forces with Imperial Guard and the Titan Legions rather than on their own. The same thing was true in Epic 40k as well.
Of course, most players (myself included) tended to play either IG + TL or SM + TL. You therefore saw Guard lists full of cheap bodies and mass artillery, and Marine lists full of Landraiders with some troops for holding objectives and buildings. Whilst the Guard lists tended to be good enough on their own, the Marine lists usually had more shortcomings.
If you're painting Epic to play either SM2, TL or E:A with, you should really build to the army list formations. If you're playing E40k, then the standard codex arrangement is fine (although you will want the assault troops in their own detachment).
Personally, I like all editions of the game, although SM2/TL has the most nostalgia for me being the first wargame that I played (and the only game I ever had everything painted for).