That's not a great argument at all. Assuming a rent agreement with say a 1-year term, there's a huge difference between trying to change rent in the middle of the contract period (obviously violates the contract unless it has specific provisions for this, which is also unlikely in most places) and asking for higher rent to renew for another term (which Occam's razor says presumably is happening here). A farmer renting farmland would never be leasing for less time than it will take their crops to grow, as that would obviously be an insane risk.
The better point here is on improving the property. Some rental contracts I've seen have terms where if the tenant spends money improving the property they get some kickback (part of it can be reduced from rent, e.g.). If you're improving property someone else owns for free and expect not to be taken advantage of, then I don't know what to tell you except that you're a sucker.
If there are takeaways from this post, it's either that 1) more jurisdictions should include stuff about this as part of their legal protections for tenants, or 2) don't be a sucker and give your landlord money for free.
Edit: if I wasn't clear, my point was that imo there should be better policies around tenants improving the homes they live in to begin with (because obviously nothing here was illegal)