The leverage only works for period where the market goes in a...

The leverage only works for period where the market goes in a constant direction or over a short period of time.
The more swings you get going up & down i.e a sideways market the more erosion you get.

I held LNAS over a 22 month period when the NASDAQ went up 51.9% & LNAS went up 73.6% over the same period, that's only a leverage of 126%.
But for each of those individual days the movement would have been say +225% on a positive day & probably -250% on a negative day.

So the lesson from all this is only hold leveraged ETFs for a very short period of time, it's not a matter of losing a few % each year to mngt fees.
None of this is unique to SNAS/LNAS.