I watched the full video, and what is missing from this is a comparison of bullet construction.

The 77 grain open tip "hollow point" bullet, if you were to cross-section it, you would find it has a significant amount of void behind that tip. When it hits, the tip of the bullet deforms dramatically, and the bullet starts to tumble, and that's part of why it dumps its kinetic energy more rapidly into the water mass.

The 168 grain bullet is also an open tip design, but it isn't as unstable in terminal ballistics as the 77 grain bullets, and its design is for match purposes, not hunting or military use. The 168 grain bullets have been the "match" bullets for Garand and M1A/M14 rifles for a long time, because they don't cause problems with the pressure profile and the op-rods of those rifles. The 147 grain "ball" round is closed-tip, full metal jacket, and is the M80 "ball" specification for 7.62 NATO, and is used for not only rifles, but belt-fed automatic weapons as well.

One of the other issues with this test is that they were using a shorter barrel than the 7.62/.308 was designed for, typically 22 inches.  Modern 5.56 ammo is designed for 20" barrels, ie, the M-16. The M-4 gives up about 100+ fps muzzle velocity with a 16" barrel.

If you look at "part 2" of this series, they use a 85 grain match .223 bullet on a water jug, and it delivers the sorts of results I would expect: much less energy transfer into the water.

https://www.youtube.com/watch?v=jyKcyXacBh4

An 85 grain match bullet is too long to be put into the magazine of an AR-15 or M-16/M-4, it might not even chamber in a .223 chamber (again, because the bullet is too long) and it requires a 1-in-7 twist barrel.  But look at how little energy is dumped into the water; that's the result of a match bullet, with a high sectional density to maximize the ballistic coefficient and maximize penetration over energy transfer.

When the DOD wanted to create a new round to get better terminal ballistic performance from the 5.56 over the 62-grain "green tip" FMJ with steel penetrator round (M855), they found that a "open tip match" and a void behind the tip got them dramatically higher "one shot stops" on enemy personnel than the green tip or 55 grain ball (M193) ammunition.  The military "M262" ammunition specification was developed for special operations forces in 1999-2000, and it requires a 1-in-8 to 1-in-7 barrel twist. Thus, the 77 grain OTM HP (M262) rounds are slightly deceptive - they've been designed to meet the letter of international law, but maximize energy transfer at the same time they're increasing their ballistic coefficient and retaining more energy at longer ranges.

If you wanted to see a bullet in .308 designed for both Bc and energy transfer, you might be looking at something like this:

https://www.hornady.com/bullets/rifle/30-cal-.308-174-gr-eld-vt#!/