Curious, <snip> would the TV be better or the monitor ?
Compared to your old TV, your new monitor has Quantum Dot (purer colours), a faster refresh rate, quicker pixel response time (less ghost trails), and wide colour gamut (WCG - a bigger colour palette). Some of this will make a difference compared to the TV. The QD definitely, also less ghosting. Blu-ray doesn't make use of WCG, so unless your upscaling BD player is trying to remap colours that don't exist on the BD discs and fudging some kind of pseudo-WCG experience then it's not a factor. However, if it s doing hat then the results often have an exaggerated effect (overly colourful) that's eye-catching but also unnatural.
The monitor must have some kind of built-in scaling to remap either 1080p or 2160p UHD to the 1440p monitor display. Does it also handle 24p output from the BD player or are you limited to 50/60Hz? There's a good chance your old TV does accept 24p, and if so, then motion should be smooth since the TV isn't having to add frames to fill in the gap between frame-doubled 24fps (2x24Hz = 48Hz) and the display's 50Hz refresh rate panel. Check out the player menus and see if you can engage 24p.
Whilst on refresh rate, I'm guessing here that your panel can't go higher than 48 or 50Hz with the BD source. That means you're not getting the full benefit of the 165Hz being able to display BD at 96Hz or 100/120Hz.
The sort of modern TVs with a full 10-bit (WCG) 100Hz panels tend to only come in at the upper ends of TV manufacturer's ranges. OLEDs have this. The very highest Samsung QLED and QD-OLED too. Higher-end Sony TVs, and maybe certain Hisense models, although we might not see them here in the UK. (Can't be sure without checking, and I don't have time since it's a moot point as you're comparing your old TV to the new monitor rather than looking for a new TV.
One area where your monitor is well behind new TVs at this level is brightness. The quoted brightness is 300 cd/m2 (300 nit). That's about on par with your old TV (minus any losses that have occurred over a decade of use) and budget TVs such as Bush, Technika, the cheapest Samsung, LG, Hitachi, Sharp etc models. the higher-end TVs are a lot brighter. The peak figures for some are over 1000cD/m2 for HDR material. The average brightnesses are lower, particularly for SDR material, and so would make greater impact if you were comparing the monitor to them.
Compared to your old monitor then, better colour accuracy and less ghosting. I think you'd notice this straight away. The two displays are possibly equal on 24p display, but the TV might even be ahead. It's unlikely that either can show you the benefit of 96Hz / 100Hz / 120Hz refresh, and neither can exploit WCG because (a) your TV doesn't have it and (b) you'd really need a rue 4K player and discs to get at the content.
. However, you might struggle with resolutions, if you send it HD, it might look poor as it will have to upscale itself, I assume players don't typical upscale to 1440p.
