The default size is 65 MB. Most games don't change that even though they need much less.
To say that most games use 65mb or more even if they don't need it is just plain wrong. Out of the 51 Switch games I own 46 of them have saves smaller than 65mb. Most of them much smaller than that.
1. Octopath Traveler/36.4mb
2. October Traveler 2/50.50mb
3. Echoes of Wisdom/16.6mb
4. Resident Evil Revelations 2/3.2mb
5. Resident Evil 6/0.5mb
6. World of Final Fantasy/1.4mb
7. DQ Monsters Dark Prince/9.6mb
8. Mario Party Superstars/11.6mb
9. Super Mario Wonder/10.3mb
10. Hyrule Warriors Age of Calamity/4.3mb
11. New Super Mario Bros U Deluxe/13.7mb
12. Super Mario 3d All-stars 20.6mb
13. Super Mario 3d World/1.3mb
14. Super Mario Odyssey/19.3mb
15. Paper Mario Origami King/8.3mb
16. Yoshi Crafted World/1.0mb
17. Luigi's Mansion 3/16.6mb
18. Mario and Rabbids Battle/11.6mb
19. Super Mario Party/16.6mb
20. Mario and Sonic Olympics/1.3mb
21. Dragon Quest 1/5.3mb
22. Dragon Quest Xi/11.3mb
23. Dragon Quest Treasure/60.5mb
24. Final Fantasy x and X2/64.6mb
25. Final Fantasy XII/64.6mb
26. Bravely Default II/2.5mb
27. Nintendo no Kuni/2.1mb
28. Rabbids Party/11.6mb
29. Rayman Legends/1.6mb
30. Disney Classic Games/39.7mb
31. 1-2 Switch/0.4mb
32. Lumo/2.3mb
33. Warframe/5.3mb
34. Fallguys/8.3mb
35. Asphalt Legends 9/10.3mb
36. Rocket League/61.5mb
37. Super Kirby Clash/16.3mb
38. Capcom Arcade 1/64.5mb
39. Capcom Arcade 2/64.5mb
40. Mutant Mudds/0.4mb
41. Operation Robocod/5.3mb
42. Super Putty Squad/5.3mb
43. Kitten Squad/8.3mb
44. Rpg Maker/64.5mb
45. Gems of War/16.3mb
46. Fortnite/5.3mb