1: Revolutionary socialism is virtually impossible unless the working class as a whole is facing conditions similar to the late 19th/early 20th century, and while that could happen in the future, it's not likely now, partially because of incremental gains that past generations of socialists have won.
2: Revolutionary socialism hasn't worked out well for the working class - see virtually every historical example. The trauma and chaos of systemic breaks of this sort, coupled with both internal and external opposition, has led these efforts to degenerate into authoritarian states that eventually reproduce quasi-capitalist relations. The *best* revolutionary socialism has been able to do is Cuba, which is largely a dictatorship, albeit a dictatorship that isn't *that* repressive as dictatorships go and has been fairly responsive to popular needs.
3: Yes it's not as principled to recognized that you will be going in forced to compromise but it may be more effective. Keep in mind that in regards to social issues, the incremental "long march through the institutions" has been wildly successful? Why? Because incremental changes alter the ecosystem of what is possible, even while having to compromise with what is possible. I would say, for example, that the election of Obama made the Sanders insurgency possible, because even though Obama didn't govern as a progressive, he ran and presented himself as one (albeit a pragmatic one), and that cleared space for an even more forthright progressivism to emerge (obviously not by itself but in conjunction with other historical and material factors).
The problem with left-socialism is that we're still trying to win based on ideas in vogue 50-100 years ago - basically the idea of this big, systemic, revolutionary "smashing" of the current system. But what that's really doing is shuffling the deck chairs on the Titanic; you need to build the political structures, alternative institutions, and class consciousness needed to step in and replace the old institutions, otherwise you just end up with socialist-flavored versions of the same old shit.
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