Agree with this. The punchline here is not "dependent types bad", it is "choose your battles". Isabelle/HOL pushed frighteningly far without proof objects or dependent types, from schemes to BSG, and never hit the mythical wall. What moved the needle was automation, libraries, and legible proofs, not a fancier core calculus. Lean is great, but if the toolchain bogs down and equality games leak into your day, your fancy types are like Tesla FSD: impressive demo energy, unpredictable commute (no offense to anyone who uses it regularly). Knowing when not to use them is the real superpower imho.
If you need finely indexed invariants, sure, reach for DT. For the other 95%, HOL plus type classes and locales, backed by a small kernel and big libraries, will get you to production faster and with fewer regrets. Milner's LCF insight still pays the bills. And yes, croissants are delicious, but optional axioms are a risky breakfast.
If you need finely indexed invariants, sure, reach for DT. For the other 95%, HOL plus type classes and locales, backed by a small kernel and big libraries, will get you to production faster and with fewer regrets. Milner's LCF insight still pays the bills. And yes, croissants are delicious, but optional axioms are a risky breakfast.