There we are.
For experiment, one side (let's say is a perfect player who wants the game ends in a draw for this purpose) could build all his/their/her strategy around the fact that two Knights alone can't win.
That alone proves is a draw.
Now imagine all possible draw fortresses there exist evaluated from +3 to +7 that ends in a draw, take R+P vs Q endgame just for an example to not mention other.
The resources for a draw for a perfect player are abundant.
Now imagine how broad just is a road that leads to a draw for a perfect player.
Let that sink in.
The method of elimination eliminates it all.
The leeway afforded by the fact that such an amount of greater material can still be a forced draw is definitely the best argument for chess being a forced draw, but it is not conclusive. To be conclusive, you would have to prove that black (or white) can force trades and exchanges to achieve a forced draw while down a piece, or two knights. This requires removing all pawns from play while not allowing too great a material advantage.
You could posit a forcing strategy where black plays not really to maintain equilibrium, but to immediately and solely to remove all of white's pawns and exchange pieces down to a draw, but it is highly doubtful this strategy could be achieved without losing too much material in the process. Thus, black plays to maintain parity, and if an opportunity arises to trade quickly down into a drawn ending, black can then take it...but not force it to happen.
I rest my case here