So, what can be done about this?! Imperial City would have been an option, but ZOS decided against gated access (perhaps scared their DLC would not generate enough sales if some people had to work for access)
Hence we're still stuck with lopsided campaigns and I wonder what could be done about this.
Coming from DAoC, I know that game implemented a levelling system for Keeps (also present in ESO) that made a higher level keep/tower stronger, harder to take, but it cost more points per hour (points were guild based).. hence not everything in the frontier was set to the max level, as you needed very active guilds to pay for the upkeep (all players in a guild generated guild points by doing PvP)
Ofcourse that only helps with going to Cyrodiil and not having any keeps you can port to, meaning you're stuck running from the spawn and getting ganked at the first mile gate you cross.
Still leaves the heavily outnumbered scenarios. For keep / tower defence that might be offset by giving outnumbered alliances a reduction in up keep cost and faster levelling structures, so they can hold onto a structure longer and maybe give them access to buy mercenaries (which are in the game afterall)
For open field 50v2 encounters, I don't think there is a solution.. unless the outnumbered faction can insta spawn a dark anchor.. but we already have enough PvE in our PvP to last a lifetime!