Try moving your swisscom router to a more central location. Objects, walls and windows weaken the signal considerably.

Also check the wifi channel in the router settings. You should always use a channel that is not or only slightly used by other neighbours. There are wifi analyser apps for your smartphone to check this.

It depends on which Swisscom product you have.
The new Internet Boxes Plus and Standard have dual band 2.4 + 5 GHz.
Internet Box light only 2.4 GHz.
Older products such as Centro Grande routers are slower.

Personally, I also bought the ASUS RT-AC87U and switched off the WLAN of my Internet Box Plus completely and only use the asus WLAN.

I'm satisfied so far, it offers a lot of setting options. However, as I have placed it more centrally in a multimedia cupboard than my Internet Box, which is heavily shielded, I cannot explain the difference in range in more detail. I can only say that I expected more from the wifi signal strength/range, so don't expect a miracle.

Otherwise, I can only recommend it.
You can also use it as a pure access point to expand your wifi professionally (in addition to your swisscom wifi).

Overall, it is one of the best on the market.

A repeater is certainly worse.

In the end, however, you can't expect your internet itself to be faster, you would have to upgrade your internet provider yourself.

I'm better off with the ASUS than with the Swisscom Internet Box Plus because it doesn't have external antennas. However, if there are a lot of concrete walls or electrical appliances in the way, any WLAN will fail.

It is important to place it centrally, avoid obstacles and use at least RJ45 Cat 6 cables with S/FTP or S/STP shielding.
Alternatively, I would use the ASUS RT-AC87U not as a repeater but as a wired access point.