You're partly correct – the limit of 750 orphan blocks has existed in Bitcoin Core since 2014, and it's indeed designed to prevent excessive storage usage. However, this limit does not determine the length of a chain battle (fork).
Here's what happens during a fork (chain battle), and how it differs from orphan blocks:
During a fork, two or more competing chains coexist. These chains are not orphan blocks; they have known parents and are fully valid.
The network compares both chains' total work (accumulated difficulty). Nodes switch their "active chain" to the one with more work. The other chain becomes "stale" but is still known and valid.
The 750-block limit does not apply to stale blocks during a fork. It's only for blocks with unknown parents (orphans). . There's no predetermined limit to how long a fork can last; it depends on mining power and block finding rates.
In other words, during a fork, nodes don't discard blocks after 750 blocks. Instead, they remain committed to the chain with the most work, and the 750-block limit is irrelevant in this context.