IMO rewriting happens mostly because going to lower-level of the needed proficiency/understanding - once the product why-what-how is more-or-less discovered, its code can be commoditized and hardened, kind-a. Dynamic stuff is very powerful == becomes too powerful (and "magic").

There is quite some wishful thinking around what so-called static-typing (which is actually static type-hinting) in dynamic languages, hoping and believing that declaring something Float, guarantees it being Float at runtime.. which is nonsense. In Ada, and few other runtime type-and-range-etc-checking languages - yes. But in plain ones.. nope. C++, Java, whatever - noone checks things at runtime. Most of those do not have a way to know what some n-bytes represent, hoping it matches the expected layout (i.e. type). While, say, python very well knows what each and every object is. If asked.

Of course, one can build such real-runtime checkers, and apply them where/when it is needed and makes sense - instead of blanket policy everywhere, but noone bothers. (Funny thing is, when i made one such library 15y ago, i was spit at and told to go code in java. And, even i haven't since then stumbled on pressing need to use it myself. Having 10 asserts (or constraint checks) in some 10kLoc does not justify whole library)

That said, i think something like language-verticals might be useful. And/Or gradual hardening, on piece-meal basis. At least a standartized way for going up/down or stricter/relaxed, from wherever one is.

But then my question is, what are you doing that you need to manually check for types ? I mean i get it at some point, usually at the time of user input usually you need to run checks to actually convert some input into a valid type. But once it is inside your program you don't need to check anymore because well... static typing and all that, you should know what you have in every step just at a glance

Well, if it is in my program - or codebase of (design+code but mostly) lining-and-discipline by me - i don't need them type-checks. They give somewhat fake sense of correctness, kind of over-confidence. Maybe useful here or there, but like 1% (Given any inputs from outside are gated with checks/validations/conversions). One rarely sends by mistake a single float where a Point3D is needed. But move(x,y) and move(y,x) are wildly different things and no typing would catch that (except excessive&brittle stuff like Xcoord/Ycoord as types). Needs explicit naming (not typing), like move(x=a, y=b) or smth.moveX(a).moveY(b) or whatever.