Everybody have access to every tech(factory). Some factories are almost unexistant (air factories are bad as starting ones and i never saw navy there). I think sometimes you may instantly lose the game at the start if you chose one factory and opponent builds its hard counter (Faction diversity and stuff...) or if you missunderstand terrain. First minutes can also be very crucial: you may overestimate your commander and lose it, enemy can sneak into your base, hide behind your own buildings and wreck you and that is especially awfull when unit that kites gets range bonus (some weird mechanic).
Airs are the most common choices for the second factories. Ship factory is a must on sea maps. Balance is heavily map depend, but the general rules are relatively simple, the slow units are bad on the large open maps, the vehicles are bad on the hilly maps, and the units that can't move in water are bad on the water heavy maps, otherwise you won't lose the game just because of your factory choice. The maps with mixted features usually have more factories viable.
Some units get more range on highgrounds, and a projectile may move beyond the range if it missed the target, other than that there isn't anything resemble a range bonus mechanic.
Biggest gripe is that the unit types are so mind numbingly generic from a lack of factions and the fact that every factory seems to produce it's own variant of a unit that none of them are interesting or fun.
Eh...aren't the factions in SupCom mostly have the same set of unit types with subtle differences? Zero-K units within the same role have more striking differences, and the roles for a lot of units are muddy. I think the game is somewhere between TA and RA2 in terms of unit differences.