Weight-based encumbrance works in extremely crunch-heavy games and/or if the mechanics are handled by software (either digital tabletop tooling or a computer game). For anything less than that it's much better to have abstracted systems - Pathfinder's bulk system is an example of relatively gamey and crunch-based encumbrance system.
Even when it comes to realism/verisimilitude (not that this is a core feature of D&D), weight is not enough to represent carrying capacity and the hindrance imposed by carrying things that are large, heavy, unwieldy, etc. It makes a whole of difference when considering the impact on a task (be that movement, dodging, climbing, lock-picking or performing an intricate dance with multiple partners) how the weight and volume is distributed. So a weight-based system is, in addition to being awkward and demanding, also not a very good simulation of reality. A well-designed abstract system could beat out old-school encumbrance.
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Either way, I would consider the act of not removing encumbrance as it is in D&D downright lazy and/or incompetent, if they refuse to replace it with something better. There's no good reason to keep it. From a commercial perspective nor from a design perspective.