Hey, you can rely on youtube clips and small sample sizes if you want, or you can take a look at what happened in the Finals. If Lebron kept up his regular season dominance throughout the playoffs in his career, he'd have a ring by now.
These aren't the Finals and you team is nowhere near as good, experienced or defensively oriented as that Mavs team.
Other than the series versus the Mavs here are lebron's stats for EVERY OTHER playoff series he has played in:
2011
vs CHI 25.8 PPG, 7.8 RPG, 6.6 APG, 1.8 BPG, 2.4 SPG 44.7/38.9/86.4 shooting %s
vs BOS 28.0 PPG, 8.2 RPG, 3.6 APG, 1.8 BPG, 1.8 SPG 47.2/43.5/66.7
vs PHI 24.3 PPG, 10.6 RPG, 6.2 APG, 0.8 BPG, 0.8 SPG, 46.9/25.0/82.0
2010
vs BOS 26.8 PPG, 9.3 RPG, 7.2 APG, 1.3 BPG, 2.2 SPG, 44.7/26.9/74.3
vs CHI 31.8 PPG, 9.2 RPG, 8.2 APG, 2.4 BPG, 1.2 SPG, 56.7/54.2/72.0
2009
vs ORL 38.5 PPG, 8.3 RPG, 8.0 APG, 1.2 BPG, 1.2 SPG, 48.7/29.7/74.5
vs ATL 33.8 PPG, 8.3 RPG, 6.0 APG, 0.5 BPG, 2.5 SPG, 55.6/48.1/69.6
vs DET 32.0 PPG, 11.3 RPG, 7.5 APG, 0.8 BPG, 1.5 SPG, 50.6/17.6/79.7
2008
vs BOS 26.7 PPG, 6.4 RPG, 7.6 APG, 1.3 BPG, 2.1 SPG, 35.5/23.1/75.6
vs WAS 29.8 PPG, 9.5 RPG, 7.7 APG, 1.3 BPG, 1.3 SPG, 48.3/29.0/70.1
2007
vs SAS 22.0 PPG, 7.0 RPG, 6.8 APG, 0.5 BPG, 1.0 SPG, 35.6/20.0/69.0
vs DET 25.7 PPG, 9.2 RPG, 8.5 APG, 0.5 BPG, 2.5 SPG, 44.9/35.7/74.1
vs NJ 24.7 PPG, 7.3 RPG, 8.5 APG, 0.3 BPg, 1.2 SPG, 42.3/30.8/75.4
vs WAS 27.8 PPG, 8.5 RPG, 7.5 APG, 0.8 BPG, 1.8 SPG, 42.5/26.7/81.3
2006
vs DET 26.6 PPG, 8.6 RPG, 6.0 APG, 0.7 BPG, 1.4 SPG, 44.2/27.6/72.7
vs WAS 35.7 PPG, 7.5 RPG, 5.7 APG, 0.7 BPG, 1.3 SPG, 51.0/38.2/74.6
Clearly, Lebron had a bad Finals but his history in series other than that is exceptional given who he played with and against.
Most superduperstars like have a bad playoff series and go on to be Champions. Magic and Dirk to name two.