"Better to submit too much rather than too little".

Actually, it's not.
It's better to submit the most succinct body of evidence you can. Submitting a lot of repetitive and unnecessary documents potentially only complicates things. The ECO and Caseworker will need to sift through a lot of paperwork that just won't be considered. The risk being that when under time pressures such a process may cause something important being overlooked.

Consideration of whether a relationship is genuine and subsisting is not a checklist or tick-box exercise.
There isn't a definitive list of documentary evidence required and caseworkers have discretion to grant or refuse an application based on their overall assessment of the submitted evidence.

The important factor is to submit enough to prove the point.
UKVI is looking to see that the relationship is Annex FM Section FM 2.0 Genuine and Subsisting Relationship. Worth taking the time to follow that link.

Typically you should include:-
Proof of regular and frequent contact (photos,e-mails,text messages,chat logs,leters greetings cards,boarding passes,letters, greeting cards,telephone records etc.)
Records showing any financial support/joint responsibilities
Children of the relationship and their support.
Plans concerning the practicalities of the couple living together in the UK

There's no need to submit everything. Just spread key evidence over a period of time.

At the end of the day it's a personal choice.
If you submit 20kg of evidence and the visa is granted you'll be convinced you did the right thing. Rather than the visa was granted despite such a lot of paperwork.

Be selective.