Thanks for your feedback. Are you a vocal coach cause you sound like one and yes I am Australian. I've been taking lessons for a year - not week after week but every know and then. I can do scales no problem and I find it easy on them to get into mix and my head voice but when it comes to songs I just don't have that same freedom and then when I get around F4 and F#4 thats when I have problems...It's almost like I run out of breath or something but the openness that I have in chest, I lose it when I get to those notes.
I'm not a vocal coach myself but I have been doing vocal lessons for three years now, although I did have a two year break between my first year and the next two years due to personal reasons.
From your reply, you sound like you are at the stage I was at the beginning where the scales and exercises were great but the application of it to a song was much more difficult.
I can honestly tell you that over time it's become wayyy more easier for me now but still I want more improvement for myself.
In regards to what you said about the openness of your chest, I think what's happening is you're trying to reach the notes in your chest voice but those notes may actually lie where you start transitioning from chest to mix voice.
Again I'd need to hear you do scales to confirm this but it's just a theory.
Often when attempting a song, people try to mimic the artist exactly like they do it which you shouldn't do because your tone and your range is unique and different to the artist.
John Legend may sing those notes in chest voice, but don't push yourself to do the same if it doesn't feel natural for you to sing the same notes in that particular register.
That song was one of the songs I had chosen to learn as well with my teacher and I kept trying to hit the same spots of chest voice that John Legend did in my own chest voice.
For me, transitioning from mix to head was super easy but from chest to mix near my first bridge I found more challenging.
Overtime it's become much easier for me to do but it was just learning to be patient.
What you may be finding is that the power there is weaker than you'd like and that's normal at least for now.
You're mixed voice gets stronger the more you sing in it but as long as you are training properly and safely alongside.
Apart from that it could be a breathing problem and where to take them with your phrasing of the song, but that's a whole different discussion.
I'd also recommend you start doing regular lessons if you want to notice a real difference.
Doing lessons here and there without consistency will take you much longer to get your voice where you want it to be simply because it's a slower muscle memory to develop.
Even if you just practice your scales for 10-15 minutes three to four times a week, over the course of time you'll notice a much better difference.
I did the same thing as you in the beginning and my teacher actually told me that I should reconsider coming to regular lessons if I can't keep it up because she'd be teaching me the same things over and over again and I'd be wasting my money.
Please don't feel like I'm trying to come across all pro because I am not at all, nor am I trying to say I'm really good.
Believe me I'd be the first one to say my voice is shit and hate it lol.
Just as an idea or reference, it's only been mid this year that when I do my scales and sing songs in my teacher's studio, the music stand vibrates from the resonance of my voice in some parts of my mix area.
I've been seeing her for a total of three years, with only the last two of those years being consistent.
It may be a different time frame for you because everyone's voice is different but I say this just to make an example of how much consistency and patience really helps in the long run.
That and then having a really good teacher.
Sorry for the long ass reply.
Wish you all the best and I look forward to hearing your progress through the forum if you're happy to be sharing them.