Pick Yer Poison
is a kid now, is a squid now
Being based on something and being a modernized version of something are two very different things. Here, let me put it this way:Well I watched an interview with the head designer, and he said it was based on TF2.
TF2 is a modernized version of TF Classic.
Tron: Legacy is based on Tron.
The movie I: Robot is (allegedly) influenced by the book I: Robot.
Brink's relationship with TF2 falls somewhere between the latter two, closer to the "influenced by" side.