Those "Would you rather" arguments aren't anything I really fall for. To have a heavy bag is nothing like releasing tension in the knuckles.
I also find it much easier to create a slow but strong attack, and especially effective in chords and long melodies, such as Rachmaninov op 16/1.
Mechanics is not something you "fall for". It's just objective fact. The closer the angle of a joint is to running parallel to an oncoming force, the lower the force required to stabilise that joint. Would you rather hold a long pole vertically or horizontally against vertical gravity? This is just basic mechanical fact, not metaphor or opinion. Look at the angles in your finger. A drooping knuckle requires larger forces, thanks to the exact same issues of parallel vs perpendicular angles. A drooping knuckle means the situation is more like holding a pole horizontally than vertically. If you dispute this, you should really clarify what possible reasoning could exempt this situation from basic fundaments of newtonian mechanics.
Most importantly, the consequences of these background issues are abundantly visible in practise. Take your finger close to vertical a la rubinstein and tap a table top. Just the faintest lengthening pushes the knuckle back up and stops collapse outright. It's such a small force, many people don't even consciously perceive it. Do the same with an extremely curved finger and the knuckle visibly falls down when you drop on to it unless you work the muscles very hard. You'd have to be suffering rigor mortis not to perceive the muscular work required to stop collapse, in this case. There's no significant difference whether it's the arm bearing down through a finger or a rucksack bearing down upon legs. Aligned joints are easily stabilised with less force. The more you introduce notable angles into the joints, the larger the workload becomes in preventing things dropping further still- with legs and fingers alike.
As I said before, if you're going from collapsed to less collapsed, it doesn't waste speed or energy like when knuckle closes in in fingertip during movement. So it's far from impossible that you can make it work in some situations, if you're going AWAY from a mere starter point rather than actually collapsing as the keys travels. However, you do have to work the harder from these angles, the same as at the bottom of a squat vs standing with only a slight knee bend. The important thing is to ask yourself whether you can control rapid passages with evenness and precision. If so, then play as you wish. If not, I wouldn't invite issues of chaos theory or subject your muscles to the larger forces involved in preventing collapse. The easiest way is to start somewhere non-collapsed in the middle of range and progress to being even less collapsed still. Again, it's not metaphor when I say that it's the same mechanics involved in getting out a squat. The most collapsed position requires the most effort to either get out of or to maintain against oncoming force. Any professor of mechanics will confirm that as absolute fact.
PS you phrase it as releasing tension, but that's a very optimistic viewpoint. When knuckles fall down during depression in loud playing, they send a hell of a lot of useless energy spiralling down towards the keybed. That means you have to then fight against this energy by introducing precisely timed muscular braking in the opposite direction, or keep holding generic tensions to limit movability outright. It's overwhelmingly optimistic to look merely at relaxation in the knuckles rather than at the whole picture of efforts and resulting impacts.