I'm not sure 3 1/2 ft. taller after 5 years is all that slow for even a vigorous Japanese maple like 'Bloodgood'. Otherwise as far as can be made out using only the photo you provided it looks like the tree has good color and density.

Removal of any part of the top will if anything slow overall size increase. Because the leaves of green plants produce energy that fuels plant size increase. So cutting part of your tree away will not make it get bigger faster.

tree time is counted in decades ... the only failure here.. might be your expectations that it should grow faster ...

i highly doubt the other plants are robbing a tree of nutrients ... if anything.. it would be the other way around.. and usually involves aggresssive trees stealing available water .. making the smaller plants suffer ...

for the sake of safe driving.. i might consider limbing it up .. to make sure there arent any kids hiding behind it or some such ...but i wouldnt do it solely in the hope it will make it grow faster ..

btw .. where are you .. big city name ...trees have a longer growing season in warmer climes.. just for the much longer growing season .. though a lot of trees might only have one growth spurt in spring .. im blanking on JMs in this regard ...

bottom line.. you have a stunning planting.. inside 5 years.. and you should be doing the happy dance.. and not trying to fix that which is not broken in any manner ...

ken

Do you ever water that island? I know many think that the PNW is a damp place but we really do not receive all that much annual precipitation and our summers tend to be bone dry. Periodic slow, deep watering of that small patch of soil in a sea of concrete - especially during eth summer months - should help to accelerate growth to some degree.

I would also add that rate of growth - 3/5' over 5 years - IS a bit slow. JM's grow faster when young, slowing as they approach maturity. For a larger growing upright like Bloodgood, you should expect 1-2 feet per season for the first 5-10 years.