Spren are Spikes

[Ising_the_being_of_a_stick]

Do spren and hemalurgic spikes not serve the same function? They both create a Connection that allows the user (the person with the new Connection) to utilize Investiture.

[Argent he/him]

A little bit, I suppose, but in the same way that... robbing a stranger on the street is the same as asking a friend for some cash. 

The net result of both (the receiving of) a Hemalurgic spike and (the formation of) a Nahel bond is that you end up with foreign Investiture in your Spiritweb, and that foreign Investiture allows you to do manipulate the power of creation. In one case you are just stapling the ability or attribute you are interested in to your soul, and now you have it; in the other, you have to work with another sapient being to the point where your souls merge a little bit, and both of you get some benefit from having foreign sDNA.