Magic might be a slightly misleading term, but it does set the correct mindset for this explanation (or perhaps aether energy). We'll just use the term energy from here on.
The energy itself is universal. It exists in all living things. Dragons are unique in that they posses the innate ability to manipulate that energy, and that energy is converted to a particular type depending on the dragon's type (fire dragon = shoots fire). Their physical form is an anointment to converting that energy into something visible and tangible.
On a biological level, (with some exceptions) every dragon has systems that internally convert energy, and adapt to the energy in a specific manner. For example a dragon that breathes fire, is also adapted to operate at temperatures much higher than normal.
Magic is different, in that it studies this and manipulates natural energy through less natural means, and in the right hands it is more efficient, it allows more things to be done.
Dragons may use this method as it does not require intense study of magic, to be able to produce desired effects, infact it is very popularized because it can provide many quality of life benefits. For example, a hand held plasma cutter, where instead of requiring a machine, clamps, and ionized gas, a specialized tool is instead attached to the user (perhaps the maw), and it converts the energy from the dragon directly to plasma through normal respiration.
Some of the largest limitations of a dragon's ability to make an effect more powerful, is largely dependent on age, and their size. Physical size affects the size of one's energy pool, and Dreu-kin are effected by this the most, and thus one of the major contributors to why they are viewed as weaker beings. With age come wisdom and thus a greater understanding of one's self over time. It's been shown with some rare beings that have lived a much longer time than most dragons, Aturis, Venuit, and Drarus are three such known dragons that have immense amounts of energy present within them, even Drarus a very elderly dragon who became a Dreu-kin. Many say during that time, he was the most powerful dragon known to them, and becoming a Dreu-kin has removed this status from him, but many would believe due to his age, his power is still greater than most adult dragons.
Arsenal Suits tend to interfere with the 'harmonics' of spell casting, thus rendering spell casting impossible to use. In order for one to be capable of spell casting with an Arsenal Suit, it requires the following criteria.
Though this is the case for the majority of spells, there are certain rare cases where a spell does not need any of the following to be cast and for the most part may be cast under most conditions.
To understand the Arsenal Suit and it's armor types. Click here.
If an RP fight ever occurs, the official limit is only a single attack or spell per pose. Also keep in mind that spells require preparation, especially if they are more powerful, so they can be interrupted if an opponent decides to actively attack you forcing you to move.