Some perspective.

A 3 star SR (just about ANY 3 star SR) will blow your 5 star R out of the water.

A 3 star SSR (just about any 3 star SSR) will blow your SR out of the water.

I have a really leveled up R. Meng Ting.

Level 72
7 Stars
72 in all skills
Date level Blue 11
Equip : all green 1 (the only unboosted stuff)
Spirit Power : Mind 46, Strength 45, Technique 45
Her stats are this :
Battle Power : 41,950
Attack : 4790
HP : 28226
Defense : 2482
Init : 228

My 3 star Chen Li SSR (not the most powerful SSR by any means) is more powerful... BP 45,965 (both BP's are without IOTs on either of them), Chen's dating level is Purple 10, 3 skills at 72, level 72, equipment level 40 or 45.

So, with minimum stars, same level, skills upgraded to same level, and only equip/dating increased on Chen Li, she's got 5K more BP.

My main SSR (Ashikaga Mako) is also 72, 5 stars, 5 skills at 72, equip level 65, and dating maxed, is around 80K BP (84,144, but has about 4K in IOT boosts). So, the same effort on SR/SSR will net you MUCH more in the way of BP.

I only have Meng boosted because I'm at the point in the game where I have left over resources and boost my SRs/Rs out of boredom while I wait to draw new/more SSR shards.