I kind of like the current approach.  Using SONAR as the base with the ability to choose other tools.  If Cake were to get serious about providing this functionality they would either have to invest a ton of resources in development, or strike a deal with a 3rd party.  The former would almost certainly increase the cost of SONAR to users.  The latter would make casual users happy, but would go unused by some as they either don't need it or would choose a 3rd party tool anyway.
 
I didn't see Matrix View mentioned.  I've never given it a serious go ... is it not useful for this kind of thing?
 
 

Matrix View is good for firing cells, but not modifying contents or recording to them. MV also has the advantage of looping content while still working/recording a linear track in Track View.

I like to think of Sonar as a platform which can be used to take advantage of other great tools.(3rd party plug ins)
You cant compare Ableton or FL studio to Sonar because they are different set ups for different things.
I wouldn't use FL studios to record a Rock band. or Ableton to Record a Jazz band.
Sonar is good at a lot of things. But im not sure sampling is its main thing.
Thus the need for a 3rd party plug in. I've mentioned it before how I would like to see a good sampler in Sonar
(I mean a full tilt up to date sampler) but im perfectly happy with using 3rd party samplers or Session drummer 3 for my needs.
 
The way I look at it is, if your looking for a Sampler to do half decent professional, or even novice home studio work,
Maybe Sonar shouldn't be your first tool. Ableton or FL Studios should be.
however with Sonar, you can do Pro, Semi Sampling stuff. you just need a 3rd party plug in, or what Sonar has supplied for years to do it.
 

Cake has done a pretty good job of sample/loop handling.  Loops can be dropped in the time line - if they aren't acidized you can groove clip them in-situ.  The Matrix is a nice sample/loop player, although it needs work, more control and better integration into SONAR.  There are lots of posts about that and we are still waiting for the promised refinements to come.  Beatscape is closest to a sample player, but Cake left it half baked and most of us couldn't get it to sync up and work correctly.  I did make an entire song out of the included loops, which were excellent.  But if I remember, it didn't do much editing.
 
Again, what I'd really like to see is the iPad Scratchpad app for Win as a module within SONAR.  Scratchpad, although simple, is a great concept, with columns that play different parts of a section and rows that plays different sections.  If you had more rows and columns that could follow or lead SONAR itself, edit the samples/loops, and if you could record into the pads live (or at least make it easier than matrix to record new combinations of pads (render column A [or highlighted pads] to a single file) you'd have more than a scratch pad or an arranger.  I still think such a critter could give live a go for the money and drag in a lot (more?) DJ/electronic types, kinda like P5 did.
 
Finally, Cake does come with a sampler - DimPro - although it doesn't edit the sample itself, which I gather is what the OP wants.  I've always thought CAKE ought to have a stereo editor, even if it was just the SONAR engine restricted and built-in.  Part of having a separate stereo editor is getting the mind into edit mode, not DAWing.  I do all my sample editing in Sound Forge, not a sampler.  I think many of us do it that way and it would be nice to keep it all in SONAR.
 
Now, on to others' wishes for SONAR fishes.

Glyn Barnes
I suggest the TX16WX a free and very powerful sampler http://www.tx16wx.com/

This was worth reading the whole thread for. Wow, that's seriously a pretty deep looking sampler for no money at all!
 
 

Anderton
I think there's a possible disconnect here. It seems the OP wants a lean, simple way to store samples and trigger them, not necessarily a full-blown, big deal sampler like Kontakt (and I don't think it's necessary to re-invent the wheel anyway). 
 
In addition to the aforementioned DropZone, Session Drummer is good for one-shot samples. But Cyclone is great for that kind of thing - it even has its pads laid out in the usual 4 x 4 matrix, so you can trigger it with all those zillions of controllers that have 16 pads. The main limitation is the pads don't respond to velocity, but the compensation is the way it can work with loops as well as one-shots, and lets you re-arrange slices. If it was velocity-sensitive, it would be a fantastic VI. Beatscape is a similar "matrix" sampler, and does have velocity. Some people find it unstable in their systems, but I don't have problems with it.
 
I feel part of the perception of SONAR not doing this kind of thing is that the program did groove/loop/sample-oriented stuff before a lot of others. For example it has always handled REX files superbly, even better than Reason until fairly recently. But because it was "so long ago," people overlook those solutions, and that's also why - even though they're perfectly functional - they're perceived as "long in the tooth." 
 
Finally there's Rapture, which does the "big boy" sampler features - keyranges, velocity switching, positional switching, etc. Although limited to six simultaneous samples, you can do a lot with those samples.

 Ah the often forgotten Cyclone which I believe was ahead of it's time.  FL, Live,Studio One have samplers but they don't get much use if you have Kontakt.   Wasn't there one in Project 5?

Bruh, I've been saying the same things for years. But, Sonar seems to cater more toward traditional musicians than those of us who use this kind of sampler as the base of our creations. Nevertheless, it's a hole that the bakers should plug if they want to move beyond the perception of Sonar not being up to snuff for serious music/beat making.
 
Don't get me wrong, I love Sonar. And, I'm hoping this will get addressed soon. Here's my original post about the topic:
http://forum.cakewalk.com/Please-Please-Please-Give-Us-A-Pad-Based-Drum-Sample-Player-m3197050.aspx

My vote for the update of DropZone and Cyclone.

I still miss the workflow that Cakewalk's own Project 5 had. I know some of it was supposed to be integrated into Sonar but it still did not have the same workflow that P5 had. I wish Cakewalk had not abandon it. There are times I have thought about trying to install P5 to see if it will work on a Windows 10 system. The sampler wasn't very easy to use but I use a 3rd party sampler.

timp410
There are times I have thought about trying to install P5 to see if it will work on a Windows 10 system. 

I've heard that it works fine with Windows 10, but only addresses one core in multicore systems.