Both sides suffer from shell and ATGM shortage and inability to suppress/destroy air defences, which drives suboptimal adaptations. An FPV drone assembled in a garage from aliexpress components and a tesla battery [1] with a submunition extracted from a cluster shell [2] is more effective than a single old howitzer with 10 shells per 2km of frontline [3], but it's a pretty low bar.
The 10% estimate is not mine, it's from a legitimate expert who regularly goes to the frontline in Ukraine.
[1]: An amusing anecdote from that podcast: Tesla battery packs are a big source of batteries for FPV drones. The packs can be sourced for next to nothing from totaled Teslas, and individual cells are very reliable.