What are you trying to analyze? Use an analysis method that matches the harmonic style of the piece you're analyzing.
Roman numeral analysis was developed to analyze diatonic functional harmony in the major/minor key system.
In Roman numeral analysis the Roman numeral designates the chord root.
The Arabic numeral figures indicate the intervals above the bass (not necessarily the chord root.) Certain figures are often assumed and not listed. For example
7 implies intervals
7 5 3, or
6 5 3.
The specific qualities or chords and intervals are determined by the diatonic key signature.
So, symbols like
V7 are understood to mean diatonic seventh chords rooted on the tonic and dominant in root position. As diatonic chords that means the diatonic seventh chord rooted on the tonic is a major seventh chord and the one rooted on the dominant is a dominant seventh chord.
Some, but not all Roman numeral analysis, uses letter case to indicate is a chord third is major or minor, upper case for major thirds and lower case for minor thirds. Additionally symbols like
+, etc. may be added for qualities like diminished (triad), half-diminished (seventh chord), or augmented (triad).
Older examples of Roman numeral analysis tend to use us upper case Roman numerals and more modern systems tend to use letter case and lots of marking for chord quality.
You need to know what system is being used.
ii7 could mean the same thing: a minor seventh chord rooted on the supertonic, depending on the system being used.
Roman numeral analysis was developed before jazz. It is not meant to be a lead sheet tool like jazz chord symbols. If you are looking for the "classical" equivalent of a lead sheet, the more appropriate thing to look at is figured bass.
It helps to understand the historical context behind Roman numeral analysis and the harmony style it was meant to analyze. You really need to go back to Rameau and the advent of chord root theory. When harmonic thinking shifted to chord roots, part of the revelation was understanding much of harmony was roots by descending fifths even if the bass and other voice movements were not moving by fifths. Labeling the chord roots with Roman numerals then becomes a convenient way to clarify such root progressions. Chord roots were the first concern.
Harmonic style at that time was more prescribed that later times - especially when you compare it to Ravel, jazz, etc. - and a lot of detail could be assumed in the Roman numeral analysis. For example, if a harmonic passage in a minor key was labeled
II V I, using older Roman numeral analysis, the assumption would be diminished supertonic chord, major triad of the dominant, minor triad of the tonic. Such assumptions could be made, because at that time playing in a key followed certain conventions. The analysis just followed suit with those conventions.
I think Roman Numeral analysis should take some cues from jazz chord analysis and become a bit more explicit.
Some harmony textbook authors have. But there isn't one universal system. It depends on what their texts are trying to cover. You need to understand what those authors are trying to illuminate, especially if they are trying to cover both the common practice era, which was concerned with diatonic major/minor keys, along with modern style using impressionistic, modal, or jazz harmony.
I have Kostka/Payne's Harmony, which uses plain
7 for dominant seventh chord, and labels like
Dom in places, like
IMaj7, for clarity. Their text also includes analysis of a very chromatic passage by Chopin and the analysis is done with both Roman numeral and alternative analysis. The chromatic passage is labeled with letters and qualities like
A♭Dom7 D♭M7, but also uses an ellipse to represent the long, non-functional passage as
I ... iiø7 V7 I. I particularly like that use of an ellipse, because it keeps the focus on function in diatonic major/minor keys.
Personally, when I have tried analyzing music after the common practice era, something like Debussy, I have used a combination of methods that seem to match the musical passages. In Debussy there are sometimes
V I type progressions, and when the musical thought behind the music seems to be cadential harmony, I label it with Roman numerals. Other passages may be more chromatic, so I might use jazz chord symbols. In such passages I look out for sequential designs and label them, or I might just label the interval progressions of roots (or the bass.) If a passage is "exotic", modal, I might just label the scale or mode.
Analyze with methods that describe the thinking and design behind the music.