Full disclosure: I am a student of Scott Lee and a certified SPF instructor. There are many thoughts I could share on this topic, so the following is not intended to be an exhaustive discourse.
You can absolutely be a good player with either a pendulum or a piston stroke. If you are already a world-beater who never misses and has great CB control, then you should just keep on keepin' on.
For the vast majority of us, however, consistency tends to be the thing we lack or desire the most. Consistency is the result of consistent (and hence repeatable) motion. The pendulum stroke, and SPF, are all about developing consistency and repeatability, of both the stroke and the shooting process. The ultimate goal of a pool stroke is to deliver the tip to the desired point on the cue ball, along the desired line, with the desired speed. A pendulum stroke is the simplest way to achieve this goal consistently by developing a repeatable (and measurable) stroke.
Along those lines, the only thing that truly matters is the moment of contact. Nothing you do after the tip strikes the ball can affect the outcome of the shot. So the notion of dropping the elbow to "keep a level plane" is unnecessary. In fact, the action required to do so introduces more joints and muscles. The more moving parts you have, the more that can potentially go wrong. That being said, since nothing you do after the tip strikes the cue ball can affect the outcome of the shot, then it follows that IF your elbow drop does not begin until AFTER you have struck the cue ball, then is not actually affecting the shot. Again, it is an unnecessary motion that adds physical complexity to your stroke, and it is harder to self-evaluate your stroke in that case, but under those conditions an elbow drop does not actually hurt your results.
As far as SPF (Set-Pause-Finish) goes, the pause between the backstroke and forward stroke has a purpose. Let's consider the stroke from a kinesiological standpoint. First, when you pull the cue back and then send it forward, you are changing directions (better known as "transitioning"). When you transition from moving in one direction to moving in the opposite direction, there is a moment when backward motion has ceased and forward motion has not begun. It may be extremely small, but it exists, and that moment is "the pause". What SPF does is take control of this fact and make it a deliberate part of your stroke, which enhances your control and rhythm. And we are not talking a very long time here - a half a second is plenty. Pausing also aids with the point below...
The second thing to consider is that the backstroke employs the tricep while the forward stroke employs the bicep. The pool stroke is really two motions, backward then forward. Pausing gives your brain and your body the time it needs to transition from focusing on the tricep motion to the bicep motion. When I work informally with folks, adding a short pause at the backstroke is almost always a "quick fix", and I have yet to see it fail to improve someone's shot making.
Another thought has to do with being either "process oriented" or "results oriented". Results are important, no doubt, but when evaluating, developing, and practicing the stroke, I believe in being process oriented. I would be wary of relying too heavily on whether you make a ball or not, or get position or not, when evaluating your stroke. Remember that once you strike the cue ball, you can't control the results, and there are plenty of things that can cause a shot to miss that are not the stroke's fault: choose the wrong english, or too much english, or not enough english, or fail to compensate for throw, or use the wrong speed, or simply aim poorly. My personal demon is failing to implement my full routine on an "easy" shot and missing, which is a mental lapse. Other common causes are dirty balls, excessive humidity, chalk on the cloth, poor cloth conditions, a slightly out of level table, etc. - all of which can cause a well stroked shot to miss. I'm not suggesting that it happens a lot, but the "rub of the green" is a very real thing.
Finally, most people don't have the training or knowledge to be able to self-evaluate their stroke, so the old idea of pulling yourself up by your bootstraps isn't particularly helpful. Spending some time with a qualified instructor can go a long way towards improving your game. I know some people don't agree, and I'm cool with that. At the end of the day, all an instructor can do is provide you with information - it's up to the student to act on it.
