My grow tent has a lot of light, but it still pales in comparison to even filtered sunlight. My ficus trees grow all winter, but I generally cut off most of the winter growth when I put them outside in the spring. It is just not good quality growth!
I think the advice you have read is for trees in refinement, where the dense canopy might make it difficult for artificial light to penetrate, leading to dieback in the interior. Your tree does not have this problem. Neither do most of mine, but I do have a fairly developed ficus pertusa bonsai, new to me this year, that should probably get that treatment when it comes in.
The biggest benefit that you would gain from a top cutback on yours would be the opportunity to position your lights lower down, giving the lower branches more light as a result. If the top grows into the lights over winter, just keep it cut back to prevent burning.
This has a beautiful trunk line, btw. It should turn out to be a nice bonsai!