What you say is true, but the need to exhaust hot air from the case is much greater than the risk of sucking warm air in from the sides, especially when the GPU card is under load and dumping hot air from the sides of the heatsink in the case, and at a fast rate.
If the bottom fans are intake, they will push back that GPU hot air and even worse, recirculate it and even increase risk of self-heating.
I tried it in my Dan A4 with 2 bottom 90mm fans, and it's confirmed, my CPU and GPU temps were slightly worse by about 2C on CPU and about 4C on GPU when then bottom fans were intake than when exhaust.
So I would recommend exhaust instead of intake, especially if you put your GPU under load often like when gaming.
If not, I don't think it makes much difference, intake or exhaust.
