Are you aware that the Mikrotik has a 9dBi 60 degree antenna built into it and unlike an external antenna to a internal 4G router there is no signal loss for cables.
I am, though on band 3 the gain is a bit less at 7dBi.
There are yagi antennae that will theoretically give me ~17dBi of gain, without being stupidly hard to point (35 degree).
In the place I can mount the antennae and router I can get the cable length probably as low as 15cm. So I don't think I'll have a lot of line loss to deal with.
I messed about with an external antenna to 4G router and the SXE LTE Kit, the SXE performed better by miles for me, it wasnt very scientific but the Mikrotik is the one I made the effort to install outside properly.
The Huawei that I've picked up also has a better category of LTE modem than the SXE LTE Kit, whether that will make any different or not I don't know.
The likelihood is that I'll never get around to it, especially as the yagis I'd need seem to be hard to buy in the UK (more popular in the US, Australia and South Africa for obvious reasons), so I'd probably end up having to build my own.
I've never built a yagi before, though I have built a couple of antennae for VHF frequencies, which worked out ok.