Smaller cut-off wheels are available in sizes — 2", 3"
Wikipedia: "Discs for pneumatic grinders are much smaller. … That is because pneumatic grinders can be powerful while being small and light, because they do not contain heavy copper motor windings."
Note that all pneumatic tools are very loud, likely too loud for residential use.
This reddit comment: "Angle grinder disks are 'Universal' these days. 125mm = 5 inch, 115mm = 4 1/2 inch. 100mm/4 inch grinders use 16mm/5/8in center holes."
4" wheels with a 5/8" hole are meant to be used on a 4" pneumatic or 4" electric grinder with a 3/8" or M10 arbor (threads). The centering flange is 5/8". 4.5" angle grinders are meant to use 4.5" wheels with a 7/8" hole. They can also use thread on 5/8-11 attachments. The threads (arbor) are 5/8-11 but the centering flange is 7/8". Thicker 4" wheels with a 5/8" hole may fit on a 4.5" grinder but may be slightly off center as shown in the video. A 4" cutoff wheel will not center at all."