So far I'm only rank ~21 or so and Leon is probably the character I'm worst with, but I find the lifesteal much more useful than the backstab. Just like you said, it gives you the edge in an otherwise even matchup. If you're low then killing neutral creeps or even two small enemy creeps will get you back up pretty quick. Honestly though I really suck with Leon so that might be it.
edit: also, I can't wait for the new character, partially because there will also be a balance patch and hopefully they give Yuri some nice stuff so he's less bad. Part of the problem is that his mines have such a delay, they should drop much faster. Maybe let him move faster when flying. Or tweak his time warp, maybe a bigger default range. I dunno.
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