Lets start with Newcastle - in a world where FFP was effectively enforced, what happens to Newcastle this summer? The answer to that question should be fairly easy to reach, we've already seen it start with Brighton, we've seen it happen to Leicester after they had some success, we saw it with Southampton 6-8 years ago, we see it happen in the Budesliga every year. The vultures will circle and pick their squad apart because in a world where you can only spend what you generate and that rule is enforced, Newcastle could never pay the wages required to keep their best players. Newcastle's entire revenue for last season was just shy of £180m, that's roughly 50% of what Liverpool, City and Utd pay in wages each season.
I did mention your Brighton example in another post. Brighton would have no choice but to sell their best players if they qualified for Europe because they're losing money. Their last two sets of published accounts show, even once you deduct the impact of covid, a loss of around £80-100m - under FFP which you want enforced, they could only lose £30m(ish) over 3 seasons!
I'm not sure if you just long for the days where Utd had a huge financial advantage over everybody else or whether you genuinely believe that under FFP a smaller club could realistically compete but either way, it's nonsense. A club with revenues of £150-180m cannot, without the help of divine intervention, expect to grow to a level with clubs that have 4x their revenue. Your Brighton's of this world do not have the fanbase or global appeal to ever generate the revenue that Liverpool and Utd could. Brighton's total commercial and matchday revenue totals around £25m - Utd's was around £350m. No matter how well Brighton do, that gap will never close, not in your life time or your kids.