Both players are important, no doubt, but the Toffees maintain a hazardous amount of debt that continues to soar. One player almost certainly had to go, and most sane business models would demand Baines, given his age and contractual status, be the man sacrificed.
The fully tied-down 25-year-old Fellaini will maintain his perceived value for several windows to come, while the soon-to-be 29-year-old Baines, with less than two years on his current deal, certainly won't.
However, such is the gulf between the actual on-field value and importance of both players to Everton that selling the Belgian was the only route to take.
Baines defines how Everton play. Every attack seems to have his influence on it at some stage, and most moves are either centered around creating him space, using him as a decoy or overloading his channel.
The Toffees defenders are used to compensating for his forward dashes—the midfield continually move the ball in attempt to buy him room—while the attackers either prepare for his delivery or look to link up with him.
His remarkable statistics are becoming very familiar with football fans, especially the ones that portray his elite creative production. He contributed 116 chances last season, the most in the Premier League, and a mammoth 24 percent of his side's overall return. Finding a player to replace that sort of workload at left-back is virtually impossible.
Baines also sent in the most accurate crosses in the division and played more minutes than anyone else for Everton. He also had the most tackles, attacking-half passes and touches, too.
Taking all that away from a side could be hugely destructive. It would require a substantial period of recovery and could potentially derail an entire season—hardly a fair scenario to burden Roberto Martinez with during his first season.
While Fellaini was also important, nothing he contributed comes remotely close to deserving the same "irreplaceable" tag reserved for Baines. Sure, Everton will miss his aerial ability in the final third, but if anything, Martinez will now try and limit his side's direct play. The Belgian's ball-winning skills will also be a loss but not in the same proportion as losing Baines' creative production.
Gareth Barry and James McCarthy are adequate replacements for Fellaini and arrive at a £10 million profit from his sale. Finding a similar replacement for Baines that could also provide Everton with a profit is surely impossible.
While Fellaini often got lauded for some dominant, imposing displays, he was never a consistent threat at Everton. A late goal often glossed over a patchy game or masked his struggle to maintain possession. For £15 million, a club record, the Toffees would have expected him to regularly be their leading performer, which he certainly wasn't.
Notably, in five years, he's never been close to taking home Everton's or the fans' Player of the Year Awards. In contrast, Baines has been awarded five of the last eight.
Very simply, when you are that integral, regardless of market rates, the Toffees had every right to stretch Baines' asking price to ludicrous proportions—which £20 million for an almost 29-year-old left-back certainly is.
Everton had to make a financial exception with Baines, ignoring what may have been the more sensible business option. The ramifications of selling him would have been too severe on the starting XI to even contemplate, and the club are now poised to offer him a new lucrative deal to recognise his value.
With Everton having fought so hard to keep him, Baines must remain a key player to build around for the next few years. He's the Toffees' most important feature and deserves any financial token that comes his way.
Statistics via WhoScored?