pdfs should certainly have more robust means to prevent tampering I agree. pdf integrity assurances aren't much better than ROT13 is for cryptography.
From what I remember the PDF standards groups are currently investigating adding something just for temper detection.
And many certificate authorities sell such certificates but for high prices.
Typing in the name or signing with a touch screen is actually considered a valid and binding, official signature in most countries. It is the lowest form of a signature equivalent to a written signature.
Agreed on cumbersome, I have a PNG file with transparency containing my signature and use Xournal++ (https://xournalpp.github.io/) for placing it on the PDFs. That works fine but still takes more time than I want to spend. But it's faster than typing it out every time.