it seems to me that playing bass is 3 dimensional... well, i guess that would be true for any instrument. the 3 dimensions being pitch, time/rhythm, and dynamics. some may be more important that others depending on context, but there you have it. combined they sum to the feel of a bassline.
pitch is obvious and doesn't need much explanation. it's the first thing anyone ever learns on an instrument. regardless of time or articulation, if you hit a note and you're making music. how fantastic.
time and rhythm would be the next leg of the wobbly tripod. this one comes a little later in our musical development and is often the piece that's most attributed to feel and is almost always in reference to intentionally playing behind the beat. i dunno. this often gets some weird mystical quality like the bassist has some weird magical powers over space and time and... maybe, if you're Pino, and you have access to a very particular type of artist and a very high level. but for the the rest of us it's getting snapped to a grid these days so i guess just learn to play on the beat and save an engineer some work. it still takes effort and work with a metronome or otherwise attentive practice with a drum machine. nobody will complain if you show up on time.
that leaves dynamics. this is the last leg to be considered and/or developed. people can go their entire careers without giving it an ounce of consideration and do quite well for themselves. in a time where everything is so gridded this may be the best way to add feel and personality to a bassline. it also is kinda difficult to develop. sure anyone can add dynamics to their playing but if it hasn't been developed it will sound spastic and unfocused and likely just bad, objectively speaking. in my opinion it has to be developed to the point of intention to be functional. as in, you intend to accent the 1's and 3's, only the downbeats of a straight 8th groove to give it an extra pulse, or a more complicated rhythm to perhaps accent the kick.
dynamics has been a focus of mine for months and the daily focused practice of it is paying dividends. it had for so long pretty much gone under my radar, it's one of those things that's hiding in plain sight. classic misdirection our attention is often diverted to more high-profile topics, like rhythm or gear, a colossal aspect of playing goes unnoticed. when it did come to my attention i immediately knew the potential and wanted to develop it for myself, unfortunately, it found it hard to get started with practice. any attempts i made were too difficult and any progress was so negligible it was shelved for something a bit more fertile. i had tried to work it into my routine several times with no success but luckily i finally was able to crack that nut.
now granted, i'm still in the early stages where i still need to actively work on a particular song part for days on end running my variations on it until it's comfortable enough. it's a long way from being an inseparable aspect of my playing but i've gotten to the point where it is now a tool i can use. the ability to add it or withhold it with creative intent is a wonderful place to be.