Just be aware that you are cutting the strength of the line by about 50% when you put a knot in it. When use an eye splice you retain over 90% of the original line strength; and usually the eye does not fail unless it was chafed through.
I used to make climbing equipment and I have tested this on a rig many times. Food for thought; rock climbers routinely take soaring whippers on 10mm ropes, never held with a splice, always a figure 8. Their lives do depend on the knot.
A bowline is ~ 55% strength, probably what you heard.
The trouble with a figure 8, and why it is not so popular on boats, is that once loaded hard it cannot generally be untied. Oh well. A figure 8 never fails unless cut through.
I can spit out 90% strength knots EVERY TIME in 10 seconds, probably with the lights off. Is the reliability of amateur splices better than that? How would you feel about falling 30 feet onto your splice? I have done that on knots.
Note on tuck back; a figure 8 can be increased in strength from 80% to 90% by taking the tail around behind the standing part and tucking it into the previous turn. Most knots fail on the first sharp turn, and this pads the turn. Some call this a Yosemite finish. A further improvement takes this another turn. Please see the attached.American Alpine Institute - Climbing Blog: The Figure-Eight Follow-Through
Climbers don't know all the knots, but they have learned a few very well.