Your thoughts pretty much sum up my philosophies and what I'm getting at with Halo 4 1-sided too. We have similar opinions but I enjoyed Valhalla or The Pit with one flag or one bomb very much. I agree tailored maps like zanzibar or burial mounds or relic etc are far better for one sided but the Halo 4 maps can easily accommodate 1 flag too.
Having 1-sided OBJ now in Halo 4 to me would be a better experience than what we play now in CTF, which is mostly 2 flag asymmetrical on larger maps than previous titles. Realistically apart from Forge maps we're not getting any new developer made maps so we need to work with what we have.
Further with full teams/parties vs. randoms 1 sided games help force the teamwork and create a better experience. Rounds also alleviate OBJ holding for 15 minutes straight while providing more structured engagements.
Here are some quick ideas for 1-sided flag and perhaps some neutral flag too:
ABANDON: The one flag could be at either location marked. The top base position would most likely become fast captures once the flag was taken but make for solid defence to take the flag in the first place. The open ended flag position would also make a great defensive setup but most likely result in easy grabs with harder run progress for the middle portion of the run with a relatively easy cap at the end via side routes or lift to capture point. No good for anything neutral.
EXILE: Either base could be the flag location but I choose the blue base for the flag location because for me or my regular team in CTF or previous Halo OBJ that is just too easy to capture. Red base offers a solid defensive setup but once the flag is taken to mid the game is pretty much over. I think the open ground in front of blue base serves as a "force teamwork" location both for offence and defense more than the blue base. No good for neutral.
LONGBOW: Both blue and red bases for Longbow suffice in one sided OBJ. Neutral doesn't look too great at Arch but could be placed at Trails as well. Overall this map would play great as 1-sided and have plenty of room.
MELTDOWN: The top and bottom aspects of this map would create interesting "force teamwork" for flag runs. Neutral could be interesting on the Light Bridge and is about equal in distance and cover usage etc. Overall both red and blue could be used for 1-flag but I feel the Fire Valley open area would create issue in taking the flag successfully for runs.
VORTEX: Easily red base for the flag position for defensive openers and plenty of paths and opportunity for runs/counters. No good for neutral.
COMPLEX: I find this flag location perfect for defense and forcing teamwork to steal a flag and get a good run going. The open areas at Silo & Modem create opportunities for ranged flag kills and there is plenty of vertical play over flag run paths too. Would work well with a variety of AA's in 1-flag. IMO not suited for neutral play.
ADRIFT: Nothing wrong with going at a neutral flag in lower mid. Hard to get up to the capping levels and creates a rush for flag or sword in the opening. Again I personally would play one-sided symmetrical here but I didn't mark it as I'm out of time for today.