Regarding dynamic range and high ISO
For the specific application you're inquiring about small differences in overall dynamic range really doesn't make that much of a difference. Most of the scene is equally dark and the few very bright spots (such as theatrical light cans that can be seen in the frame) are often going to blow out at any exposure that doesn't make everything else way too dark.
How well a camera can shoot in low light with high ISO and still produce low noise images does make a difference. Based on personal experience I'm not sure how well DxO's high ISO score (DxO Mark is the source of Snapsort's sensor numbers) differentiates different cameras with fundamental differences in how and when they apply noise reduction. Cameras that do on-die noise reduction do better in DxO's ISO test than cameras that wait until after the analog-to-digital conversion to apply noise reduction because the former has the benefit of the on-die NR while the latter does not get the benefit of the post ADC NR as tested by Dxo Labs. And while 1385 vs. 919 looks like a huge difference at 50% higher, remember that ISO is an exponential scale - 1838 would only be one stop better than 919. ISO 1385 is barely more than a half stop faster than ISO 919.
To see any significant improvement that will make you go "wow" you're going to have to go to a full frame sensor. Even then it will still be a struggle to shoot in such challenging environments as you'll find in most small music venues and get clean images. Will there be some improvement using a D5300 or D3400 (both newer technology) over a Rebel T2i/550D? Sure there would be. The newer technology and the slightly larger size of the Nikon APS-C sensor will make a difference, but it will be very incremental and not revolutionary. There would also be some improvement, although perhaps not quite as much, by going from a Rebel T2i/550D to a Rebel T6i/750D. There would be even more improvement going to the recent EOS 80D. You'd need to go to a full frame model such as the 6D Mark II or 5D Mark III/IV to compare to the FF Nikon 750D.
Regarding differences in AF systems
A "cross-type" AF point is really just two single AF points superimposed over each other. Typically one is sensitive to contrast in a vertical direction, the other is sensitive to contrast in a horizontal direction.
The number of cross type AF points isn't much of a consideration in a dim club. Most small clubs are dark enough that your AF system will struggle. Regardless of how many cross type AF points a camera has, the center point will always be the best performer because it is getting the most light (assuming the lens is not severely out of alignment).
When using lenses faster than f/2.8 Canon's center AF points give better sensitivity and performance in low light than when using slower lenses. The disadvantage of such points included in their higher end models is they don't function much at all above f/2.8 and so Canon uses two cross-type points at the center: one sensitive up to f/5.6 vertical and f/4 horizontal (or f/8 vertical in very high end models) that is oriented in the normal horizontal/vertical pattern and a second sensitive only at wider apertures up to f/2.8 that is oriented in a diagonal "X" shape. The lower tier Rebels only get a center cross-type point tuned for f/5.6 but Canon says, "With an f/2.8 or faster/wider aperture lens, the center point operates with greater precision." The faster lens doesn't improve AF performance as much as it would with a "dual diagonal cross-type" AF point in the center like some of Canon's other cameras have. Most of Nikon's entry level cameras have normal cross-type AF points, even at the center, that are optimized for f/8 or f/5.6 and using a faster lens doesn't provide much additional benefit.
Regarding shooting practices
I frequently shoot bands in small venues. Some have better light than others, but it's a challenge to shoot in all of them. Even in larger venues where there is brighter "theatrical" type lighting it can be a challenge. In the dim venues I shoot with a full frame Canon 5D Mark III (previously a 5D Mark II) and my two lenses of choice are the EF 50mm f/1.4 and the EF 135mm f/2 L. In the brighter "theatrical" settings I can use a stabilized 70-200mm f/2.8 on a cropped sensor 7D Mark II (and the 7D before it) and also use 24-70mm f/2.8 or even a 24-105mm f/4 with image stabilization on the FF body (handy for when shooting from spots affected by the strong vibrations coming from the massive speakers - and don't forget your earplugs!). But I rarely even carry the f/2.8 zooms to shoot at dimmer venues. For more on lens choices for various types of venues, please see this answer to What are appropriate lenses for concert photography?
I almost always use the center point only when shooting bands. I use the AF-ON button (you can remap the AE Lock button (*) to do the same thing on your t2i) to obtain and lock focus and then hold it while I recompose and shoot several shots with the focus locked at the same distance. I also use manual exposure mode. With the FF camera I can push ISO up to 5000 or even 6400 but I shoot most of the shots I take at ISO 3200. With the APS-C camera I don't like to go beyond ISO 3200.
I always save the pictures in raw format. You can get a lot from an image that doesn't look like much straight out of camera by using the powerful tools that raw processing applications give you.
For an extended discussion of how to get the most out of limited gear please see this answer and the comments to I'm having trouble getting sharp pictures while shooting a concert from a press pass location.
