You kind of need the bots to get stuck to even have a hope of beating this game mode. I don't see why people are worried about abusing obstacles when its practically a requirement to win...
The difference is the way the bots get "stuck"
A good map is where you can leer the bots to a roof/hut/barn/bridge etc. However without a player there to leer the bots they will go straight to the virgin/viscount.
eg yaragar, istiniar, rizi, Pagundur, Kulum, Haen, Buvran
A bad map is where the bots get stuck behind a tree/rock/etc where even without player interference some bots wont make it to the virgin/viscount.
eg Glunmar, Bulugur, Buillin, Azgad
Some have both which makes good maps, ok but annoying eg Aldelen, Serindiar, Burglen
So yes, you need something to draw the bots away from the virgin/viscount. However, anything that completely stops the bots ruins the map. So, if you use stake and siege shield to block access to the virgin/viscount every map becomes "winnable" but it will be boring and abusive.
We need more maps with tactical locations (burns/huts etc) not equipment we can deploy for 'easy win'.
One of the best features of yaragar is that the fence is low and glitchy. This means that the bots can still shoot and swing at players and occasionally bots get past the fence.