Browne has been immense this season, and I'd love for him to sign on again based off how good he's been this season. However, the last few seasons before this one, he was not performing head and shoulders above the rest of the team to warrant his wage being the top earner. So it doesn't surprise me if at present, the club have offered him less than his current wage. After this season he's had, I'd offer him the same as what he's on now, but before that, I'd have said less is fair.
Also the same thing was said last season about how on earth are we going to replace someone of DJs quality for free. We replaced him with Mads, not for free. Not sure why this notion has come about again with Browne. Especially when the club have said it'll be the first COVID free season in regards to the PSR books.
I personally don't consider anyone we have as irreplaceable. We don't have a single player who would comfortably walk into a Leicester, Leeds or Southampton starting lineup. Never mind being a PL starter. That's when I'd start to maybe consider someone as irreplaceable.