The Top 50 (Tier 4) is an oddity. These are the decks from the top 50 ranked players. Some of them have set up farms to give you easy/free rare cards. Others are using their usual decks, while some are intentionally designed as anti-player decks. They are mostly or all upgraded cards, but because players can (do) set up farms, the game gives you the un-upgraded versions; rare cards are worth decent money, but you face half the False God difficulty (fully upgraded deck) without the increased reward.
The most annoying thing is decks designed to slow things down. There is first the usual dichotomy between speed and control in CCGs: the basic plans are to burn down the enemy now or keep him from doing anything and then implement a late-game plan. If you are farming, you play for speed, because your goal is to get as many wins (cards) as possible as fast as possible; speed vs. speed, speed vs. control, and control vs. control are all potentially interesting matches. Some T50 decks complicate that by never really intending implement that late-game plan. They just want to annoy you. The amusing ones go heavily for life gain. They might have an attack or two, but mostly they are really big punching bags that heal themselves. The most frustrating ones are large decks that plan to seize control and never do anything until you run out of cards. That is the late-game plan: counter everything and hope the player has no way to prevent decking out. The deck’s secondary objective is winning, in the sense of defeating the player, although some of them are rather good at that (remember: fully upgraded, designed by top players, and no cards “wasted” on offense) unless you have very fast control or damage. The deck’s primary objective is to take as long as possible. The deck-builder wins if you, the player, want to stab him in the throat as the game drags on.
In PvP, this is a perfectly viable approach. Even without Millstone-equivalents, building a huge blob and taking the punches can be a winning strategy. You get the bonus of watching frustrated opponents seethe. I have seen several versions, including one explicitly named “Rage Quit.” But if you play one of those in PvP, you must sit there as long as your opponent. Heck, he might have his own control deck, with both of you expecting a long game. When you set it up for the computer to control, you are just making a land mine filled with glue, waiting for players to get trapped. You don’t get to see them wriggle, unless they post on the forums about how much they hate you, but you know the computer can spring the trap on dozens of innocent victims at once.
It kind of makes me feel bad about NanoStar Siege. While deciding it wasn’t something I would play in the long run, I noticed that you could improve your defenses with in-game coins without leveling up, and that there was a daily reward for logging in (and for winning or losing when others attack). I could log in occasionally, collect cash, and upgrade the increasingly ridiculous defenses. Yeah, go ahead, pick on the low-level account for easy points. Go for it. Too bad for the people looking for even-level opponents who hit that.