I'm shocked that nobody has said this yet but:
1: YES! You DO need dismount to kill capable pvprs now. Proliferation of healing abilities, potions, petals, apples, trapped boxes, etc etc etc. You must curtail the ability of your target to escape if you want to close the deal.
2. NO! Archery dismounts are NOT ok! Archery already has the utility of mele from 8 tiles away - dismount is nearly game-breaking. To the gentleman above who said he thinks archery is balanced because you have to dismount your ethy first: If you ride an ethy, you are not a serious pvpr. Period. Mele dismounts require timing, proximity, teamwork, etc. Still a powerful special move, but not the 8 tile away nightmare it is for archery.
3. The solution is simple! Require heavy XBOW dismounts to be within one tile. Add a simple error message that says "From the distance, your blow would lack the velocity to dislodge your opponent". Done. Nice, neat and tidy. Archers retain the ability to dismount, but must get within a reasonable range and expose themselves outside of a group. Additionally, a mounted player has the ability to recognize and read the situation and decide if approaching the archer is worth the risk.
Easy fix for EA, balance does not extend below or above the current mele levels, and we solve a lot of issues with perma dismounted tamer/archers. Everybody wins.