I can't really see these pictures. I know which one you are talking about for the first one. Where Lucy was saying Natsu was cute while he was sleeping.and then she got punched.
Teammate cheering? Not sure about the other one either?
First before arguing anything. I want to just point out this is a relationship created by Mashima. Who had a boy bang a girl in a 12 year old boy after like 3 meetings. So Mashima might not be the most logical guy when it comes to romance. He also had Elle and Haru become canon by Julia stripping Elle (taking off her bra) at a party to get Haru to confess. Then he had Musica and Reina become somewhat canonish by her dying.
It has been established in the manga repeatedly that Lucy cares for Natsu more than a friend.
Now you have pointed this out with the "at best it is a one sided crush."
I can totally see this. It has been my case for most of the series that Lucy has had a crush on Natsu. The problem with the ship is him. He's not completely tsundere to her affections. Plus they are best friends. He is just kind of there, receiving them without encouraging them.
Thus the issue comes from his lack of acting romantic. So scenes like this are really...
Just pure friendship....
Now Lucy on the other hand has shown more than that. Jealousy is not a friendly emotion. It is a possessive emotion because if you are "just friends" there is no reason for you to get jeaous over your friend looking someone else over.
Lucy has also shown to be more worried about Natsu than other teammates. Like in Edolas, Lucy did not check on Wendy the 12 year old, she ran to Natsu while Gray went to Wendy.
To which in Alvarez, Happy even had to remind her about Juvia and Gray.
Sorry Graylu fans.
Lucy rubbing Natsu's back and not Wendy's.
Lucy was unhappy with Natsu for leaving her.
Also she was more depressed by Natsu leaving than other people leaving like Gray and Juvia who also left. And even the guild breaking up did not inspire this level of reaction.
I personally prefer these type of moments that are small, which hint at romance as oppose to over the top displays of affection that lack real romantic feelings.
Now stuff like this is fan service
Now you are completely right about Natsu (or Mashima dropping the ball from Natsu's end).
As for Natsu.....
We don't have many blantly romantic moments for him. The closest moments are things like this...
This moment that was a Natsu intitiated touch to calm Lucy. Could this be friendship? Maybe. Does it lean toward more romance? Maybe. The fact is that Natsu goes out of his way by petting her head (and this wasn't a fanservice moment either). She was questioning why he had not told her about Future Rogue and Gray.
Also this hug from Gmg is lost easily in Mashima's drawings. But it is clear that is Natsu initiated. Everyone is celebrating. And Natsu throws an arm around her to cheer. That is inclusion. Is it friendship? Maybe. Also noted is the only other person doing something like this is Bisca who has an arm around Alzack's.
Also Natsu truly enjoys being around Lucy. As shown when he formed a team with her.
Probably because she jumped out of a cave for him
Honestly Mashima had a good reason for them to be partners. Natsu inviting her to the guild and then (taking responsibility in looking after her) but Mashima never explained it that way. And I (as a Nalu fan) admit that.
The biggest Natsu moment was him giving her his cloak
We don't know why he gave it. We don't even know if she asked for it. We just know that he did not give it to Gray or Erza who were both barely covered.
And we know that in Rescue Macow arc, he did not want her to take his blanket.
I also believe the cherry blossom tree was meant to be taken romantically by Mashima.
Natsu was the one who remembered their fated day.

Speaking of Lucy getting her guildmark. In chapter 2 he acted like he didn't care
but really he was totally aware of Lucy getting her guild mark.
Natsu also kept Lucy's maid costume and made special momentos of his moments with Lucy.
For Natsu to make notes like this. He would have to really find these moments special. Lucy's face clearly says it is something special which is why she cleaned his house.
Thus the main problem I have with Nalu is that Mashima portrays them really caring and cute one second but then kind of comedy/shallowish the next.
Look at this.
This panel from GMG does not really scream romance.
There
could be feelings, but Natsu would want to save any friend more than he would want to fight. And also Lucy herself is blushing, but she is doing it in a more "I'm acting trying to poke fun at you way."
Mashima's inconsistency
He has perfect moments he could build on, but he doesn't. Another problem with Nalu is that a lot of good moments are Lucy initiated and we either do not get Natsu's reaction or we have a lack of reaction from Natsu. Which I guess could be tied back into the fact we do not get any building on these moments. SO I will have to agree with you. They get a lot of fanservice moments. They also get a lot of close friendship moments that get taken out of context by fans.
^Moments like this scream romance. And not in that cure "childish crush/playmate" way.
We just have the ball being dropped. Mashima had the perfect opportunity to build from this moment, but Natsu lost his memory of. We have no building of his thoughts and feelings from Lucy "dying." And it was not an issue that got brought up in "Natsu's heart." Mashima does this every arc. Even this arc which is suppose to be the arc Mashima is writing them as "more than friends and less than lovers but it is the same moments (moments initiated by Lucy, fanservice, Lucy worrying over him, reverse back hug, Natsu worried about Lucy) that is shown every arc.
So my argument is not that they don't have romance. You just have pollution of the moments with so many moments that are based for other reasons than showing their bond like the fanservice, the friendship moments, the crushy stuff, Lucy blushing at him.
So mostly as a Nalu shipper, I wait to get Natsu's POV on this.