The OP states prison is a good map because the team with more squishies is easier to gank, therefor making it somehow better than other maps. Prison does not offer any lanes to allow characters to level without being constantly harassed. Prison is so small that just some boots of speed or anklets of speed allow you to go from 1 end to the other end before a flag can even be captured.
Prison favors characters that get early stuns, and characters that have heals and high damage output from level 1. Tower rook, erubus, QoT and unclean beast are all characters that if put together in prison in literally any order, will generally outperform the opposing team.
Reasoning that move speed plus and move speed decreases are more effective on prison is just bad logic. These abilities are good on all maps and against most DG. Just in prison if you get slowed, the whole team can be on top of you before your able to escape to safety, and towers are so weak in this game safety is generally at your crystal. This basically means you HAVE to go BoTF favor. This is not what makes a good map. A good map should require coordination between team members, but it should require much more strategy than just combat between demigods. This game is based around mobility, defense, offense, creeps, citadel upgrades, itemization, and skill builds. These all combine together really well on maps that have lanes (AKA mimic the original design of the game as close as possible) because the game was designed in this multidimentional way.
Playing prison is for people who don't really like playing the game, but just want to hose over players with unfair advantage and tactics on a horribly broken and badly thought out map.
To make prison viable it would have to be 2 times wider and 15 - 25% shorter. Thus spreading the flags further apart and allowing more run time between them, and giving both teams better escape routes to there main base. It was really bad design to set it up the way it currently is.
QFT. The only "strategy" on Prison is to maximize Level 1 effectiveness and blow people off the field immedeately.