well if u r going wide and taking a slightly later apex, that normally means u r driving on the faster line. so if some one dives up the inside then they r off line, and effectively have no line to "take" from you,and if they manage to t-bone u, then normally u r further into the corner then them, so u have the line.
As said earlier the real cars do the pressure driving, at the start of the race, u r not allowed adefensive line, but if near the last few laps they r then allowed to use a more defensive driving if they r a slightly slower car.
But it has to be within reason
It does not mean doing the sways down the middle of main straight, it more means as they move to drag down the side of u, u can move over a bit as a defense, but do NOT sway majorly, but if u have a major line behind, i feel let the truly quicker guys go past.
Its not a job, its a bit of fun really, and if u block for to long, people get annoyed and will the shunt u off line, enough to cause damage even, so if u r a fair bit slower, just get off the line and let them go, its not like u take home a couple of thousand dollars if u win like the Real car drivers do.