It should be obvious that the waveform update rate depends on the record length and not the sample rate. Thus it’s not fair to compare 10 Mpts on the Siglent to a DSO that can only use a total of 2 Mpts in run mode.
Furthermore, Keysight MSOX-series is optimized for speed; in fact, everything else is subordinate to this. Functionality is implemented in hardware in the Megazoom ASIC, which is blazingly fast, but also rather inflexible. By contrast, on the Siglent there’s always some processing time for the data, which pauses the acquisition. And if speed and waveform update rate are really that important, anything other than a Keysight Megazoom DSO will be a disapointment.
The average waveform update rates for the SDS800X HD can be found here (reply #2, section “History & Sequence Mode”):
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/msg5293747/#msg5293747Instead of complaining about the update rate, most engineers would be excited about the analytic capabilities they get with the SDS800X HD and the many things it can do, which are beyond an MSOX3000, such as:
True 12 bit resolution.
0.5 % accuracy.
Custom probes.
Permanently visible 7-digit trigger frequency counter.
True 500 µV/div full resolution sensitivity and not just 4 mV/div and software zoom below, which would not be so bad on a 12-bit instrument, but with only 8 bits it certainly is.
<2.4 nV/√Hz voltage noise above 1 MHz when 50 Ω terminated.
Deep memory up to 100 Mpts total, which is not halved in run mode.
History recording permanently active in the background, where past trigger events can be looked up and analyzed to our your hearts content.
Deep math and measurements up to 10 Mpts, not just 32-64 kpts.
Up to 4 math channels incl. FFT and formula editor.
FFT up to 2 Mpts.
Measurement statistics with Histicons that can be enlarged to histogram windows.
Track Plots.
Bode Plots, up to 3 channels and up to 120 MHz with frequency selective detector and AGC, providing more than 100 dB dynamic range.
Last not least: the price!
For anyone not caring for these features, Analytic (Siglent) scopes in general are not for them.