sp att: 104
sp def: 71
Blaziken's base stats:
sp att: 110
sp def: 70
The only major difference is speed.
As for move pool, they learn 58 of the same moves. Blaziken can learn a total of 79 moves, Infernape can learn 85. They share more than two thirds of their move pools. Coupled with having very similar stats and the same typing, they're almost as similar as two Pokemon can get.
Also, Brongong is heavily defensive while Metagross has high offensive stats. Roserade is somewhat similar to Venusaur, but has lower Attack and Defense while having greater stats on the Special side. If it had been the final form of a starter it probably would have been called a rip off, however it still isn't as close to Venusaur as Infernape is to Blaziken. Gyarados's best stat is attack, which happens to be Pelippers worst stat, the only stat that is anywhere near close is defense, and that's still over 30 points off.
Long story shot, I know my shit, Infernape is VERY similar to Blaziken, Blaziken came out first, Infernape was made in his image. Your arguments about other Pokemon being as similar as they are are invalid.