I am on big baby #2 both off the charts (1 from birth, the other by 2mo) Both weighed 8kg (18lb) at 4mo & 10kg (22lb) at 6mo & for both I got them to close to 6mo (first was 5 months 3 weeks) with just breast milk... with #1 I had to feed 6-7 times/24 hours, but with #2 I actually really only did 5/24hours as he did for the most part 10hours overnight.
What I did do for #2 was double offer at all feeds... would feed & then 10mins later offer again... this was mostly as he gets really distracted by big brother & also as he is very fast & a 5min feed is not quite enough, but 7mins is if that makes sence.
Anyway I do think some babies can benefit from solids before 6mo... but just wanted to say despite HV advice it is possible for babies above the 98% to get to 6mo with just breastmilk & sleep through the night.
I also believe (after 3mo) - growth spurts for BF actually don't increase the volume but change the "content" so by introducing solids rather than "feeding through the spurt" the balance changes, so if you introduce solids at a growth spurt, it won't stop as quickly as if you feed more often for that "spurt"... the body is uniquely balanced like that... they need more solids to make up for what bm would have given, had a spurt been fed through. Does that make sence.