When a battery vents it vents through the top of the battery unless some other portion of it is damaged. Yes, personally I'd rather have it facing down with a free path for gases to exit. Top or bottom vent holes would be safest, depending on battery orientation. Holes somewhere in the side could be blocked from swelling. Relying on enough clearance for gases to escape around the battery to reach vent holes is kind of a bad idea. Ideally the top of a battery should have a straight shot for gases to escape.
Some of the mods I own are tight enough a thicker battery wrapper is enough to block the rapid escape of gases from a catastrophic failure, which in turn could lead to further blockage due to swelling. Most of the newer designed mods I have offer pretty decent paths for gas escape. Many of the older ones I have not so much.
A mod such as the XXX or the new SubZero X are about as safe as a mech can be. Both offer great paths for gas to escape in the event of a blow out.
As for sleeving, it offers an extra layer of protection, but you should inspect your batteries regularly for damaged wraps regardless. Lack of a sleeve on the Admiral is not something I would personally consider in the purchase.
Common sense and education are essential to getting along safely in life, vape gear is no different.