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SeedRandom[1]
data = Join[RandomReal[1, {300000, 2}], RandomChoice[{0, 1}, {300000, 1}], 2];
Dimensions[data]

{300000, 3}

nbins = 5;
binlims = Through[{Floor[Min@#, .01] &, Ceiling[Max@#, .01] &}@#] & /@ Transpose[data];
binlists = BinLists[data, xbins, ybins, {0, 2, 2}];
binmeans =  Flatten /@ Map[Mean, binlists[[All, All, All, All, -1]], {-2}];

cft = Charting`FindTicks[{0, nbins}, {0, 1}];
MatrixPlot[binmeans, DataReversed -> True, ColorFunction -> "Rainbow",
  FrameTicks -> {{cft, cft}, {cft, cft}}]

With nbins = 25 we get

SeedRandom[1]
data = Join[RandomReal[1, {300000, 2}], RandomChoice[{0, 1}, {300000, 1}], 2];
Dimensions[data]

{300000, 3}

nbins = 5;
binlims = Through[{Floor[Min@#, .01] &, Ceiling[Max@#, .01] &}@#] & /@ Transpose[data];
{xbins, ybins} = {##, -Subtract[##]/nbins} & @@@ Most[binlims];
binlists = BinLists[data, xbins, ybins, {0, 2, 2}];
binmeans =  Flatten /@ Map[Mean, binlists[[All, All, All, All, -1]], {-2}];

cft = Charting`FindTicks[{0, nbins}, {0, 1}];
MatrixPlot[binmeans, DataReversed -> True, ColorFunction -> "Rainbow",
  FrameTicks -> {{cft, cft}, {cft, cft}}]

With nbins = 25 we get

SeedRandom[1]
data = Join[RandomReal[1, {300000, 2}], RandomChoice[{0, 1}, {300000, 1}], 2];
Dimensions[data]

{300000, 3}

nbins = 5;
binlims = Through[{Floor[Min@#, .01] &, Ceiling[Max@#, .01] &}@#] & /@ Transpose[data];
{xbins, ybins} = {##, -Subtract[##] / nbins} & @@@ Most[binlims];
binlists = BinLists[data, xbins, ybins, {0, 2, 2}];
binmeans =  Flatten /@ Map[Mean, binlists[[All, All, All, All, -1]], {-2}];
{xticks, yticks} = MapIndexed[{#2[[1]], #} &, #] & /@ Range @@@ {xbins, ybins};

MatrixPlot[binmeans, DataReversed -> True, ColorFunction -> "Rainbow",
 FrameTicks -> {{#, #} & @ yticks, {#, #} & @ xticks}]

SeedRandom[1]
data = Join[RandomReal[1, {300000, 2}], RandomChoice[{0, 1}, {300000, 1}], 2];
Dimensions[data]

{300000, 3}

nbins = 5;
binlims = Through[{Floor[Min@#, .01] &, Ceiling[Max@#, .01] &}@#] & /@ Transpose[data];
binlists = BinLists[data, xbins, ybins, {0, 2, 2}];
binmeans =  Flatten /@ Map[Mean, binlists[[All, All, All, All, -1]], {-2}];

cft = Charting`FindTicks[{0, nbins}, {0, 1}];
MatrixPlot[binmeans, DataReversed -> True, ColorFunction -> "Rainbow",
  FrameTicks -> {{cft, cft}, {cft, cft}}]

With nbins = 25 we get

SeedRandom[1]
data = Join[RandomReal[1, {300000, 2}], RandomChoice[{0, 1}, {300000, 1}], 2];
Dimensions[data]

{300000, 3}

binlims = Through[{Floor[Min@#, .01] &, Ceiling[Max@#, .01] &}@#] & /@ Transpose[data];
{xbins, ybins} = {##, -Subtract[##]/5} & @@@ Most[binlims];
binlists = BinLists[data, xbins, ybins, {0, 2, 2}];
binmeans =  Flatten /@ Map[Mean, binlists[[All, All, All, All, -1]], {-2}];
{xticks, yticks} = MapIndexed[{#2[[1]], #} &, #] & /@ Range @@@ {xbins, ybins};

MatrixPlot[binmeans, DataReversed -> True, ColorFunction -> "Rainbow",
 FrameTicks -> {{#, #} & @ yticks, {#, #} & @ xticks}]

SeedRandom[1]
data = Join[RandomReal[1, {300000, 2}], RandomChoice[{0, 1}, {300000, 1}], 2];
Dimensions[data]

{300000, 3}

nbins = 5;
binlims = Through[{Floor[Min@#, .01] &, Ceiling[Max@#, .01] &}@#] & /@ Transpose[data];
{xbins, ybins} = {##, -Subtract[##] / nbins} & @@@ Most[binlims];
binlists = BinLists[data, xbins, ybins, {0, 2, 2}];
binmeans =  Flatten /@ Map[Mean, binlists[[All, All, All, All, -1]], {-2}];
{xticks, yticks} = MapIndexed[{#2[[1]], #} &, #] & /@ Range @@@ {xbins, ybins};

MatrixPlot[binmeans, DataReversed -> True, ColorFunction -> "Rainbow",
 FrameTicks -> {{#, #} & @ yticks, {#, #} & @ xticks}]