Saying the block meter is bad design because its luck based is akin to saying drawing cards randomly is bad design. When drawing cards, it certainly sucks when you get the worst cards ever and you opponent gets the best, or for example, if your starting hand is just full of high casting cost cards, but because we draw cards randomly, the games play differently. You can also build your deck in a specific way to increase the odds of getting the cards you need when you need them, for example, by having lots of low cost cards and only a few higher cost cards. Another example is the first play. Do you play that arm wrestler first turn against sunflower if the odds of them having a card that will destroy your wrestler are about 50%? There is nothing that you can do to control this, and neither can the opposing player, it's pure luck, and yet it makes the game interesting.
With the block meter it's very similar. If you see your opponent plays creatures with low attack, you should usually not block them, since this will fill up your meter at a low cost to you. By the same rule, you should avoid using low attack creatures unless they have Bullseye. By doing this you are essentially mitigating the luck factor. The fewer hits you make, the less dependency you have on wether you get 1, 2 or 3 shield segments added to your opponents shield. But at the end of the day, luck rules the outcome and you can only play your cards to increase the odds of getting a good result for yourself while reducing the odds of a good result for your opponent.
When the shield segment gets close to filled, there is even less luck involved. If there are 3 segments left you know that there you have a higher chance of NOT hitting the block on the first hit, so that is where you place your biggest attacker. If there are two left then assume the first hit will likely be the one to hit. Sometimes the result goes against the odds and you get unlucky, just like you sometimes draw badly, but if you play to your odds, you will be successful most of the time, which is how card games work.
By the way, when there is just one segment left, there is still luck that you have to account for, and that is the power they will draw. You have to know which powers your opponent's avatar has and if they have already played any so that you know which one they might draw and then think about how that might affect the board. Then you have to position your creatures and play your cards based on the probabilities of any of the possible given plays and how they could affect the board. This is exactly how card games are played when referring to just about any card effect that has incomplete information and is part of both the fun and the strategic challenge.
