I play with a pick and with fingers and I can tap and I can funk with my thumb. I play in an original heavy at times and mellow at times band. I play with what the song sounds best with for me and my tone. I have been playing over 28 years and I dont claim to be incredible but I can hold down the low end and I get asked to play often by other respected musicians in my area. I dont feel less than when I use a pick or fingers it doesnt even enter my mind. Anyone who bashes a technique or a means of playing in a full generalized way has a lot to learn about being open minded and having some professional respect.
For me to even address another player because he made a stupid comment about fingers or picks or whatever is so much a waist of my time they dont deserve me to even acknowledge them and frankly I dont care what they think or if they gig or sit in their bedrooms doing nothing. They are stuck in a mindset they feel they need to defend or to be able to put something down because inside they truly dont have full confidence in their own playing or knowledge of music or what it is to be a musician. I hope only that they will grow into a more professional or wider minded prospective but chances are they wont and thats ok too. Enough about small people with small thoughts.
As to what sounds heavier it depends on many factors and is more than just simple plectrum or not. First regarding the fingers or pick the attack and percussive sound of a note played by a pick can vary how you hold the pick. If you choke up on it only leaving the tip exposed it can smooth and fast especially when playing closer to the neck. Letting more of the pick exposed and playing closer to the bridge can get a very hard percussive punch. Chris Squire actually hits the string with the edge of the pick and the edge of his thumb and has a completely unique way of playing with a pick and has his own tone and sound completely. Versatility is also huge as it is with many forms of finger playing.
My Warwick NT 5 string thumb to me when I play it sounds huge with my fingers and wimpy when I play that bass with a pick definitely on the D or G string. My Zon Sonus with humbuckers sound freaking killer either way. I get the overall feeling that when I play a bass with humbuckers or MM pickups they tend to lend themselves better to a pick and single coil or stacked jazz pickups sound better to me with fingers. So I actually put as much thought into what bass Im going to use with what strings as I do with I am going to use a pick or fingers. All so very subjective and unique to the individual player.
As an overall statement on famous players doing whatever on a bass just remember one thing they are famous and most likely you are not. So try to learn something from them rather than cast judgment. They too as I would imagine dont care what you think of them and how they play even more so than I dont. I will say there are many guys who can shred and play faster with fingers than with a pick. I can play more notes in a shorter time with my fingers but for me like many players I hear playing fast with fingers they must play lighter and the notes get lost and sound weak to me sometimes. Alex Webster and Billy Sheehan can play mind blowing speeds and have total accuracy and sound full and bad ass they are not the only ones but they stick out in my mind as the guys doing it right as far as fast, articulate, and most of all what you asked heavy. There are many more but this is already too long.
I believe Mr. Lemmy K sounds pretty freaking heavy as well as Jason Newstead, Justin Chancellor, John Campbell, Jeordie White, are a few getting it done right heavy with a pick. Get all your basses and play them both ways and decide for yourself and ask they guys your playing with what they like better. Using both is cool then you dont sound the same all the time. If you cant remember to bring a pick to a gig you probably cant remember much of anything. Good luck use your ears.