The Beastmaster isn't as good an example of a strong late game mage as a Priestess because his defenses aren't nearly as strong, and it's harder for him to keep his investments alive long enough to reach a dominating late game position. Although just a bear and multiple wolves is hardly a late game position anyway. You can reach that state by turn 3-4, although you might have to accept an unhealthy lack of defense in order to pull it off depending on what your opponent is doing.
Turn 1 (19): Ring of Beasts -> Steelclaw Grizzly (1)
Turn 2 (10): Enchanter's Ring -> Timber Wolf (0)
Turn 3 (9): FD Brace Yourself -> Timber Wolf (0)
A dominating late game position might be something like 2 Guardian Angels, Samandriel, Brogan, and a Knight of Westlock. Playing that much total creature strength is completely unnecessary against a solo rush build, but can be absolutely vital in an attrition mirror match. It really depends on the matchup.
3 Knights of Westlock is more like a midgame position than a late game position unless they had a lot of enchantments boosting them or something.
As to whether attrition strategies are viable in a competitive environment, I don't know. I haven't heard of many in tournaments, but the tournament sample size is so small that it's hard to draw firm conclusions about the relative strengths of different strategies from the data I've seen anyway.
I'm also not sure how long most people that play at tournaments would take to win with an attrition strategy, which could impact tournament viability. It shouldn't hurt the Attrition Priestess too much due to her tools for gaining a life advantage, but I can see it hurting other attrition mages.
Agreed, Priestess is for sure stronger. The problem with attrition strategies in tournaments(specifically Priestess) is that they can't stand up to attack spell Wizard, such as my opening or a better example is Tim's book. This is why I say playstyles like this rely on non-interactive games. If your opponent let you turtle all game to win then they probably would have lost anyway. Time also becomes a factor because if your control does happen to come online, it might do so too late.
That sounds like it would work pretty well, though it's 12 mana.
I've been playing around in my head with a 2 Guardian Angels + 2 Steelclaw Grizzlies setup for a Priestess. The Guardian Angels would let me spread damage around, so it would be hard to focus me or my bears down, the bears would do a ton of damage, and the high base stats on all of my creatures would make my healing incredibly efficient.
The main thing I worry about when playing a Steelclaw with another mage is having it corroded and focused down, which the Priestess is really good at preventing. It would be a little weaker against flyers than angel spam, but it would be little less vulnerable to mana denial.
The problem with this is that you're looking at a Grizzly and Guardian Angel on turn 2 followed by another Grizzly at turn 4 and an Angel at turn 6. This is assuming you are casting almost nothing aside from those. Meanwhile I get to sit back and let my investments win me the game. Guardian Angel would only be used for guard I assume, so all I would have to do is kill Grizzlys to win. It could be annoying, that's for sure. But by the time you have your Angel/Grizzly ready to do something on turn 5 I will have killed one of those creatures already.
I've had some interesting early results with Gray Angel spam. Throw in a Guardian Angel or two for defense, and just spend the first 6 turns casting Angels if you can. 13 mana for a 4die attack flyer isn't a bad deal. Don't even bother with her terrible spawnpoint, though.
The more I look at it the more it seems that intercept and creature spam are the way to go.
You're probably looking at the same problem as sdougla2 but the creatures do come out a bit faster, so that's a plus. Less offensive power though. I'm going to put about as much mana into them as you are putting them out but I'll end up winning out because I have the investments(Mostly Gate) that you wouldn't have.