My advice, as usual, is try to play battle or siege more often, instead of just DTV. If battle is too hard, then siege should do. But learning to play against other players, who have complex footwork and attacks, compared to the simple AI, is a much better and faster way of learning how to play, and, once you get the basics, DTV will become a bit easier and you should resort less to - sorry for the expression - "dumbed down" tactics like shieldwalls (constantly) and play more natural as if it were battle or siege.
But, of course, the other part of my advice is not to play DTV too much (or only), or you might start losing skills and/or reflexes that will make things hard when fighting other players. At least that's what has happened to me, and now I can admit that I can fight bots very relaxed - I played battle for a couple of years before DTV appeared - but struggle whenever I play battle or siege, because I've lost a lot of reflexes.
Seriously, if you tried to play "PvP" on a regular basis, you would sooner or later realise that DTV can be, instead of a xp-gold-grindfest, a different and fun game-mode where you cooperate with your teammates against the evil invaders that try to kill your boss. And these last changes make it a lot more challenging than before. I see the team lose a lot more often, and I think that's a good thing, because it puts us to the test rather than give us free xp and gold on a silver plate.
