Using a guided system in the pursuit of finishing with a convex is doable. Before I was comfortable with freehanding, I used to use my Lansky & DMT Aligner sets to create a narrow-as-possible V-bevelled edge first, then following with hard-backed sandpaper to 'strop' the shoulders of the bevels into a smooth & thin convex behind that crisp edge, and then polishing the convex on something like a hard-backed denim strop with some aggressive polishing compound, OR doing the same on a firm/hard wood strop.
The idea is to convex what's behind the apex, and not any part of the apex itself. Issues with the edge geometry being rounded into dullness aren't due to convexing itself, but doing it with the wrong materials or bad technique, i.e., the held angle too high or using too much pressure on softer substrates, or a combination of those things. Done properly, a convexed edge will cut like a demon, even better than a crisp-shouldered v-bevel in some uses. The crisp shoulders of V-bevels can bind in some materials, like heavy cardboard. Convexing yields even more improvement in thicker blades, if used for cutting cardboard. A convex done at good shallow geometry, with the shoulders of the edge polished, will go through heavy cardboard like a laser.
Keeping the apex crisp on a convex edge is about using methods and materials that reduce or eliminate rounding at the apex, and allowing the natural freehand variation in angle to convex only what's behind the apex, i.e., the shoulders of the edge. Bad convexing comes from using substrate materials that compress too much (mouse pads or softish leather, for example), and more so when those soft materials are also relied upon in trying to refine & finish the apex itself. Use the soft stuff to shape & polish what's behind the edge, if you want to. But for refining the edge itself, something much, much firmer will allow one to 'sneak up to' the cheeks of the apex for precise refining & thinning of the edge geometry, without letting the abrasive roll over & around the apex in the process, which is when it'll get ruined. Put in practical terms, convex right up to the edge using something very firm, or even hard, like a stone. Use this to apex the edge and produce/reduce the burr. Then, for additional convexing behind the edge, something with a little more 'give' in the substrate can be used to work the shoulders. For me, I no longer use anything thicker or softer than hard-backed denim or linen (used with compound) to do any finishing work on edges. That means I never use leather with compound, anymore.
All of my favorite edges are thinly-ground, shallow convexes shaped on stones, with edge geometry at/below 25° inclusive. Most of them come out finished with little or no recognizable 'bevels' behind the edge, instead transitioning from the thin & sharp edge grind into the upper (primary) grind in a shallow arc. They cut like devils, and are durable and very easy to maintain.
