The only significant risk here is that there is a serious weather issue for LAX-OAK which does not affect the LGW-OAK-LGW. In that limited instance, it does not matter how many frequencies there are on the first ticket.

But, I don't think that the risk shifts appreciably if you fly up to OAK 2-3 hours earlier.

In the remote chance that there is a problem, get yourself to SFO if possible and also call BA immediately. While BA has no obligation to reroute and will cancel your ticket if you no show, there is always the chance that BA is overbooked and could use your seat and might reroute you out of any number of its gateways, including LAX.