Dream bike and

Few weeks ago, i did a post and someone suggested me to do a bike first to point which geo is theorically perfect to me.

This is what i get.

38(M) 1,89m, 82kg, 907mm inseam, pretty stretch, legs slightly shorter than arms. 3rd year into MTB, 40 to 50km D+600 to 800m on sundays club rides. I want to add road cycling for winter and go for triathlon (not at a high competitive level).

My dream bike is Pinarello F, and hopefully, my local bike shop is an official Pinarello retailer.
I met the owner and he's (1,86m) currently running a dogma F size 575.
I came with my bike fit report and he gave me the opportunity to get on his bike to check for proper sizing (it was ok with a 110mm stem instead of the 120mm he has)

Here is what has been talked about:

The shop mechanic with who i talk for more than 1 hour said. He really hate bike fits/fitter because "you can get 10 results from 10 fitters and none really suits you", and i know what "taking things with a pinch of salt" means, but this is radical. i understand what the message and he isn't completely wrong but it's imo a good point where to start if like me you don't know a thing about geometry.

"As a newbie, aero not recommended",and told me that it's possible to make a comfortable endurance frame aero but the opposite would be more difficult. I heard this argument before (Cade media or GCN video IIRC) which is a valid argument because i'm not a pro and will never be. F is supposed to be the model that fits my need and goal.
Another thing he pointed out is the quality of the carbon frame, recommending a high-end tier frame with cheaper parts to begin with.

My first question is: Is he right? what are your thoughts about that? How far (with the inexperience i have) in frame tier should i go? what is is the sweet spot between not enough, good, or overkill? Will i notice differences in comfort, compliance and stiffness between frames levels?

I had 5k€ budget in mind.

At first, i planned to go for a F5, once the discussion over, maybe a X5 would be better. Next day, i tried the shop owner's dogma, told me that he wants to sell the frame is currently riding and give me a total 15% discount due to the fact that i ride in the local cycling club (which i think is kinda cool) to build something around it. (all prices announced are with the discount)

So i can have a probably overkill Dogma F, ultegra, 45mm carbon wheels for 7,9k€ which is 1,5x my initial budget but on the paper a real good deal i think.

Or a more affordable stock models:

F5 Shimano 105: 4.7k€
X5 Shimano 105: 5.1k€
F7 ultegra: 6.7k€
X7 ultegra: 6.8k€

My heart goes "BUY IT GODDAM IT. STOP OVERTHINK IT" but my mind (and wallet too) says go X5.

What would you do?