Sure, but you do seem to ignore the picture they are painting for you, the signal you have for T-Mobile when compared to AT&T at your loation is very poor, you got noticably better results when you let the router (and in some respects the network) select the bands for you, but at that point on T-Mobile you were getting carrier aggregation on the downlink and that will typically get you more throughput in most cases vs where you do not have any CA.
That doesn’t mean the mast is adequaely provisioned in terms of backhaul, although if you are seeing consistent results throughout the day I would agree is probably not the case, either that or it is permenantly oversubscribed 24/7… such things do happen.
What gives you that idea out of interest, band 71 is a low frequency band (600MHz) typically these lower frequency bands are used to deliver coverage at the macro layers of the network, not high capacity at the micro layer (ignoring what the carriers marketing department would have you believe and listening to what an RF network architect would use them for) - lower frequency will generally travel further and is typically deployed where outdoor range or delivering reliable indooors coverage due to better penetration through walls etc. is more important than outright performance compared to the higher frequency bands where you will often get significantly better data performance but at the expense of where the signal will not travel as far or penetrate indoors areas as well.
Yeah, I will add the data on it is not always accurate or current, it can give you a good idea of what you will find but it is obviously not totally reliable, for example you reckon the AT&T tower you are connecting to is only a mile closer yet the RSSI and RSRP would make me believe it is a whole lot closer than that
TST is a mobile router, have you out of the interest of testing chucked it in your car and driven closer to where you think the cell site is - be curious if you get get the performance higher with a stronger signal.
You may also need to consider the antennas you are using as if testing band 71 performance is your goal it may be worth checking they provide adequate gain across that frequency range - the stock dipoles that come with the Peplinks (ACW-813?) only offer ~1dB gain down at 700MHz and possibly do not fully cover down to 600MHz according to the specs on the website.