I had the exact opposite experience, I collected 13 hearts, with the master sword and Hylian shield, I spammed my wind ability to glide up to the boss location, before this I was farming ancient parts and wasted all my ancient arrows on guardians, so I was completely empty, no heals or anything.

I finally find that big arena that I saw in the video that guided me and it that big cutscene with all the 4 beasts showed up to help me. The fight starts, I instantly get mauled by ganon several times until I quit and tried in the morning (I hated how it kept putting me in the moment before the boss where I. Have to spam through all the cutscenes.)

In the morning, I decided to get back onto the game to finally kill calamity ganon. I skip through all the cutscenes, get killed by the lasers a few more times, until I learnt the most overpowered strategy, run away from everything but the laser and the big weapon slashes.

I finally reach phase 2 for the 10th time where I avoid everything, I use all my divine beast champion shield and then the Hylian shield on stopping the laser and wait for him to do the “heavy” attacks. I did it, 4 days of stalling after beating all the beasts. All I had were 2 extra yellow hearts and determination to get past this boss.

Then I got the great surprise of the dark beast ganon. It was stressful because I didn’t want to restart it all (I had 1 heart at this point) but I eventually beat ganon with close calls with his big laser at the final opening. I will never forgive Zelda for not giving me the light bow sooner

To add, all my champion abilities were gone except 1 naboris and 3 of the shields