That is about how long it took me to beat him. I had to look up how to beat Stage 3, myself.
I hated the Diggernaut fight at first - it seemed really cheap, Samus took too much damage, and I didn't really get why they suddenly put this tough-as-nails boss in a Metroid game when we haven't had a super frustrating boss since Prime 2.
I immediately had a huge appreciation for Diggernaut once I finally beat it. It's such a highly technical fight - you have to be spot-on with reaction time and recognizing when it telegraphs an attack, it's actually super similar to an old-school Mega Man X Maverick boss fight. You absolutely cannot beat it the first time, it's too complex for that. But you get the pattern down, practice it over and over, and before you know it, you can take it out without a problem. I think I died to him like two times on my second playthrough, because that's all it took to get me back into the groove and strategy I had figured out the first time.
Not going to defend the chase sequence though. It's really out of place, and insta-kill is almost never a good thing in any game. It's pretty much the one part of Samus Returns that I think could have been removed and nothing but good would come from it. There's other ways to build up the boss battle, like what Prime did with Meta Ridley ,what Fusion did with Nightmare, and what Other M did with Vorash.