Plenty of people will complain about the quality of Chinese made inexpensive scopes, but I don't see any reason why you'd expect them to fail in the near term. Perhaps the likelihood that they make it to a decade and are still going strong is not as good as from other makers or from eras when overengineering was more common (and the price reflected it), but I expect a good bit of my gear to last a decade with minimal maintenance, though my use case is far from 24/7/365.
If you're looking for stuff with a brand name, like the Owons you mention, there are reputable test equipment vendors that sell them as well which can offer their own warranty policy or information. A company is only going to warranty what makes sense for the lifetime of the parts inside and what parts they want to have in storage, and with increasingly more integrated and less serviceable designs, it's harder to expect that distant support... so the warranty periods aren't that extensive, even if the parts have plenty of longevity.
In terms of failure modes outside of improper use, a modern scope is probably dependent on electrolytic capacitor lifetime, screen backlight lifetime (if a CCFL, at least), fan lifetime, or maybe rotary encoder lifetime. Provided it's been designed well thermally, the reliability of construction is generally very good (and lead free solder is a VERY well understood process since it's used extensively in modern electronics, even if it's a pain to get right initially), and the lower power solid state parts used are probably more reliable than many of the solutions in equipment from the 80s or 90s... so there's really nothing making me expect that some of my newer gear won't be operational in 2025 or 2035.
As for your particular use case, there are some 12, 14, and higher bit options around - some of the newest scope designs are 10+ bits, and picoscope (PC based, but also big screen friendly) has been offering high resolution converters for quite some time. You can also adjust your range switch and coupling to see very small details in most signals, so while the dynamic range of an 8 bit scope is quite limited, you can often still see very fine vertical detail. There's also the option of getting audio specific DAC/ADC gear and using a software suite to get the displays you want - there are many options for getting bode plots on 24 bit audio signals using mid to high end sound cards and software. There's also an increasing connectivity factor in some brands, where you can take a scope and plug a function gen into its USB port and have them coordinate automatically for bode plots and such. Siglent has some options like that, but I think R&S and Keysight in particular have made a move towards this kind of integration, though you certainly spend for it.
If your tests aren't concerned with phase, you could also get your bode plot from a simple white noise generator and the FFT function on almost any modern scope. You'd have plenty of sample rate for enhanced resolution mode for such a low frequency signal range (usually 1-2 more effective bits), and the newest generation of scopes can manage a 1Mpoint FFT for very fine frequency detail.
You shouldn't have delay issues using a scope. If you use a USB one and you have some application where you need to see the signal in realtime, you may run into issues, but generally speaking, the waveform updates per second of a current generation scope are high enough that the delay from measurement to the screen is less than the several ms delay a lot of DSP hardware has, and I can't think of an application where syncing the visual with the input is all that important. If you need to check alignment of very fast changes, there's always single shot mode, and if you're trying to coordinate a signal generator with what you see (for some reason), you can always just output a trigger signal from the sig gen to exactly align where the pulse was generated with what's being recorded on the scope. Since a scope isn't really a tool for processing and replaying signals in realtime, it's for visualizing continuous ones and capturing fast transient ones, I don't think you'll ever run into the sort of 'round trip delay' issues you'd have with a DSP based audio recording and playback system.