We were earlier at 5+ weeks, so can't answer this part of your question, but hope to help by sharing our experience (sorry, long story).
Our little one was also gaining weight nicely, which is why 5 professials missed it. We had our doubts due to reflux and found a good lactation consultant who diagnosed in 5 minutes from entering our house...
We were told of the pros and cons, I'll start with the pros.
-Revision helps with drinking, bottle or breastfeeding not really important.
-It helps with weaning, as moving your tongue is important...
-It is important for speech, reduces chance for need of speech therapy
-Reduces dental issues, as you (unknowingly) clean your teeth after eating with your tongue.
-Also, your tongue normally rests against your palate and also influences the shape of your palate. A revised tongue will give less issues with sinuses etc. as a result.
- Also, little ones have a lot of muscle tension, as they try to drink and try to get a good latch. We didn't need extra therapy for this luckily, but noticed her hands and legs and feet relaxing afterwards... also, she had little blisters on her lips... (and the crying because of reflux and the enless drinking sessions and ... well).
Cons:
The revision itself, the crying afterwards and some blood. Luckily she was young and sleepy, and got breastfeeding directly afterwards.
The tongue can heal again: it is an open wound in a wet environment. In our case we were told to massage the wound every couple of hours. This is hard, our DD didn't like it one bit. And this crying broke me sometimes.
There is a chance of your little one to develop mouth/tongue aversion due to these excercises. So basically I had to 'feel' and look when I could dial back the massages. I checked how the wound looked like and how my little one was doing/behaving. In our case this wasn't standard, as -when we came back for a check up after one week- we were told they only revised it partly in purpose.
(Sorry if TMI in part below).
Hers wasn't just a thin tongue tie, but V-shaped: narrow at the front and fleshy at the back. They didn't want to cut completely, as there was a risk of nerve damage in the more fleshy part of the tongue tie. And then she might be in pain longterm...
As the wound wasn't completely healed (due to it being a bigger, more fleshy wound than normal), I had to continue exercises for a few days more. And we had a second check up also due to this.
It took a while to get the reflux under control. It wasn't a magic cure, also due to the partial revision I think, but it was so much better! No more damaged nipples for me, a better latch and less reflux for our little one!
And now?
She is 18 months, still breastfeeding every day and enjoys it a lot. I found it difficult to relax during weaning, but she eats, drinks from an open cup, babbles a lot, loves to move around. She can stick her tongue out when being mischievous, lick her lips after eating yoghurt. We are still really really happy we did this.
We also helped another couple find a good lactation consultant who sent them to this very clinic (not UK) and they also had extra months of breastfeeding and have now switched to bottle feeding for practical purposes.
Neighbours two doors down will have to wait, their little one has issues but is too old for a revision without anesthesia, so will have to see when he is older.
My dad would say: french kissing is also nice for when your DD is older 🤣
Wishing you all the best with your choice. It is difficult either way.