I've found good board placement and reading your opponents to build your card and building strategies around to be far more important. Race just makes certain strategies easier than others from the outset. Knowing what those strategies are and building around them (or purposefully feinting you are) is where the real game happens.

That is very much possible, though I do not think that factions are too versatile outside their preferred tactics.

I've played Chaos Marines like Orks and Eldar like Space Marines to devastating effect. There is enough you can change with lopsided card strategies to make any race effective with most strategies (although I would avoid trying to play Eldar as Orks or vice versa for obvious reasons).

I've played around 40 games now. Most of them two player, maybe a quarter with 3/4 players.

I believe that the Orks are strong simply because their combat cards feel like they make the most difference. Party Wagon and Biker Nobs are dreaded cards in our playgroup and we all know their name. Meanwhile there are very few cards others can name from sides they don't usually play.

It just doesn't feel like any other combat cards change the combat as much as the Ork ones do. It changes around tier 3 but tier 3 combat cards don't come out in too many of our games.

Also Eldar have fewer T1 units - I only have 3 wraithguard and the others all have 6 of their T1.

Eldar also have 6 tier0 frigates, while all the others only have 3. And ork ships suck, apart from the suicide squad they'll be fighting an uphill battle.