I've transferred dozens of my own MiniDV cassettes so let me share the methods I used and what I think makes sense for you. I'll preface by saying that this was a project that took me DECADES to get started, precisely because there are so many options and variables to consider. However, once I began I did it all at once, and was relieved to do it. This is an investment of time and money, but one you'll agree is worthwhile for unlocking and securing your tapes' contents.
First, to answer your question, if users were reporting that EasyCapViewer wasn't running well on El Capitan, then it almost certainly won't run well on Mojave. For what it's worth I downloaded EasyCapViewer and it launched without any errors on Mojave, but you can't know how it functions with that capture card hardware until you try it out. EasyCap isn't a 64-bit app, so it's definitely not optimized to run on modern versions of macOS like High Sierra or Mojave, but it does technically run. If you're dead-set on using that software, you could always get a copy of Mac OS X 10.5 Leopard, install it on a disk partition or external drive, and work with it from there.
Second, if your priority is to capture the highest quality of these videos, then my recommendation for you is to go the Firewire route, because it's the only option that transfers the pure digital signal from tape to Mac. If your intention is to archive and back up these tapes for posterity, you'll want to capture the highest quality version of that video, and Firewire is the only way to do that. But be aware that importing raw digital video can take up a lot of storage space, so depending on how many tapes you have you'll want to have a fair amount of disk space, and/or a backup drive to hold them all. The alternative is to important analog video, via this EasyCap tool or one of the many other options like it (there are many analog hardware and software tools just like EasyCap, so I encourage you to check those out if EasyCap doesn't sound like it has the support you're looking for). Just keep in mind that when you import analog video the video gets compressed, so you won't get the same quality video out of the analog transfer as you do with digital Firewire. You may not notice or care much about that difference, but just be aware that importing via analog will result in a loss of some quality that you would otherwise retain through a digital transfer. On the positive side though, since analog video files are compressed they do take up much less storage space.
Back to Firewire: As you noted, this setup requires a few adapters. In your case you would need a Firewire Cable (assuming your camcorder takes the small 4pin plug, like mine did, you'll need a 4pin to 9pin Firewire 800 cable). Then depending on whether you have a USB-C hub for your Mac (some of which do offer Firewire 800 ports, or else Thunderbolt 2 ports) you'll need an Apple Thunderbolt to Firewire adapter. If you don't have a hub you'll also need to add an Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter to make the direct connection to your MacBook Pro. Like most Apple dongles, these are overpriced, but you can find the same products on Amazon or eBay for half that.
Economically, buying a hub and/or a bunch of adapters would probably cost more than just picking up an old used Mac, like a Powerbook G4, and doing the video transfer with that. It sounds crazy but you actually might consider this option, since those models have built-in Firewire and often come installed with Tiger or Leopard, which would also be compatible with the EasyCap. Oddly enough it could be less of a headache than trying to make all the old hardware/software fit with your new MacBook Pro.
Lastly, a note (and warning) on tape damage: be aware of the possibility that your tapes may have video/audio artifacts or disruption (several of mine had sections like this, and they were painful to watch). Hopefully yours don't have any, but if they do I'll just save you the trouble of investigating the Why: it can be connected to recording in LP instead of SP, or using different brands of tapes whose tape lubricant doesn't get along well with other tape brands. A corrupted digital signal can make those sections virtually unwatchable, and importing those clips via Firewire looks terrible. In that case the best alternative for importing those sections is to use an analog tool. The one I used was Elgato's EyeTV to import those damaged sections of video via S-video or Composite video. Importing damaged sections via analog isn't great either, in that it won't get rid of the artifacts, and for some reason it reduced my LR sound channels to mono sound, but the damaged sections do import better with analog than with digital, so I used analog imports exclusively for that purpose.
I know this is a lot of info, but hopefully some of it is helpful for you. Good luck with your continued efforts!