TECL performed extraordinarily well because it was a sector the did well and because your time frame does not include any severe market corrections. Unfortunately, TECL only exists since December of 2008 so it can't be used for such a comparison. So let's consider the DJIA.
From the end of the GFC (3/09/08) until now, DIA returned 397% whereas DDM (2X DJIA ETF) returned 1,666% for better than 4X return.
However, if the starting date used is 12/31/07 at the beginning of the GFC then DIA returned 158% while DDM returned 281%, less than 2X. So why the huge discrepancy (4X versus 2X)?
For the GFC (1/01/08 to 3/09/09), DIA returned -49% while DDM returned -79%. If a leveraged ETF loses 4/5 of its value, the road back is much slower because they can only leverage that 20% of remaining value. IOW, the DIA required a 100% rise to break even but the DDM required a 400% rise to do the same.
Another issue for much shorter holding periods is the P&L due beta slippage but I'm going to pass on that explanation since your question dealt with a 7 year long term hold.