Yes, though effective gain will probably differ depending on the band used. Neither mikrotik nor anyone can produce antennas equally optimized for both bands, is a matter of physics.
Don’t be afraid to choose a device with no external antennas if suitable; for the gains used for WLANs, 10 times out of 10 a device with internal antennas (RB951 in 2.4GHz band is a great example) will outperform those with rubberduck-type external ones, as the connector and pigtail losses usually null the external one.
You also rule out one of the most common failing components: connectors and pigtails.
in fact for indoors high gain omni antenna cause the ap to get more noise and interference from environment and too wide coverage area with low overall performance
i think for indoor internal low gain antenna are best
keep in mind that internal antennas normally are 3dbi if you use 6 dbi you are duplicating the energy irradiated horizontally lowering the energy irradiated vertically, like a donut pattern, maybe 6dbi its a good limit, it depends of your implementation.
my opinion its about avoiding the “bigger its better” assumption
because that assumption some people put 10 or 13 dbi omni antennas on indoor implementations
in this link the topic its better exlained than i can do