Impression
There were a couple of timeskips within the flashback, but I wasn’t too bothered – they got the main message of the episode across, which was the evident lack of trust between the Uchiha and the Senju. To an extent, it’s true that this depends on the leader involved – Hashirama’s father was staunchly against any sort of verbal communication with the Uchiha, and thought that Madara knew everything and planned to steal intel from the Senju. Which is a pragmatic mindset for that time period – I can imagine that backstabbings and betrayals happened all the time, with everyone perhaps rightly only concerned for their survival. Had Tobirama succeeded the leadership of the Senju instead of Hashirama, I’m sure there’d have been a lot more fighting before any sort of peace treaty was concluded. It’s actually quite fortunate that Hashirama turned out to be the elder (and stronger) brother!
That being said, a lot of the future discord that arose even after Hashirama and Madara started leading their clans was due to the actions of Madara himself – the adult Madara was a very different person from the child who decided to warn Hashirama about the trap the Uchiha had prepared. It might have stemmed from his nature as an Uchiha, or perhaps from the fact that Izuna died at the hands of Tobirama. You can sort of chart his feelings from the various stages of his Sharingan – if a lack of Sharingan represents a state in which he’s willing to dream big with Hashirama, then the awakening of his Sharingan is an abandonment of those ideals, while his eventual EMS entrenched him deeper within his hatred. Ultimately, I think a large part of his decision came from the fact that Hashirama was stronger than him – even without his Sage Mode, Hashirama was able to hold his ground and eventually overwhelm Susanoo, which is just incredible considering how much of an immense force it is in Naruto’s time.
It’s not gonna last though. I bet there’s widespread pent-up resentment amongst the Uchiha, some of which might come from Madara himself. At least, his decision to eventually leave Konoha says a lot about his long-term feelings. And we know how that ended up turning out.