Another option may just using the python built-in sum function as below

Step-1:Get list of the paths of the rasters

import arcpy,os
raster_pths = []
for root, dirs, files in os.walk(raster_input_folder):
    for single_file in files:
        if single_file.endswith('.tif'):
            input_raster_pth = os.path.join(root,single_file)
            inpt_raster = os.path.join(root, single_file)
            raster_pths.append(inpt_raster)

Step-2:Now create a list of arcpy raster using those collected raster paths-it needs memorey

needed_rasters_virtual = [arcpy.Raster(i) for i in needed_rasters]

Step-3:Now do the sum

summed_raster = sum(needed_rasters_virtual)

Another option may just using the python built-in sum function as below

Step-1:Get list of the paths of the rasters

import arcpy,os
raster_pths = []
for root, dirs, files in os.walk(raster_input_folder):
    for single_file in files:
        if single_file.endswith('.tif'):
            input_raster_pth = os.path.join(root,single_file)
            inpt_raster = os.path.join(root, single_file)
            raster_pths.append(inpt_raster)

Step-2:Now create a list of arcpy raster using those collected rasters path-it needs memory

needed_rasters_virtual = [arcpy.Raster(i) for i in needed_rasters]

Step-3:Now do the sum

summed_raster = sum(needed_rasters_virtual)

Though the above method needs a lot of memory in case of large raster but it comes handy when you need to do some complex steps at easy go like-

Say you have a value list estimates = [ 0.292088680, -0.000046162, -0.000014440, -0.000023292, -0.000027125, -0.000000819, 0.000032517, -0.000021072, 0.000004663, 0.000047970, 0.000111651, 0.000008808, -0.000014821] and another raster list,say rsts of same length. Now you want to multiply each element of the rsts by respective element of the estimates list according to their position order and after all you want to get the sum of all of these rasters.I this case this way may comes handy as below-

for the above process:

rsts = [arcpy.Raster(i) for i in needed_rasters]
summed_raster = sum([i*j for i,j in zip(needed_rasters_virtual,estimates)])