Being the big DBZ nerd that I am, I couldn't resist; I bought the game probably a day after I posted this question lol.
Bottom-line up front: Xenoverse's fighting mechanics may seem more shallow that Budokai Tenkaichi 3's at a glance, but the sheer number of customization options in every aspect of this game allow you to do almost anything you want.
Every character has a light physical attack, a hard physical attack, and a projectile attack which can be used ad nausea. The light and hard physical attacks can be strung into pre-defined physical combos which cannot be customized, but which can be interrupted at almost any time with special attacks to continue your combo, or simply strung together in different combinations. Characters can also spend stamina to "teleport" behind your opponent while being attacked or during your own combos, and fly upward and downward while either locked onto an enemy or in a free-range mode.
Each character also has 7 customizable special ability slots; 4 special move slots, 2 ultra move slots, and 1 escape move slot. The customizable abilities include close and long-range energy attacks, physical combos, transformations, buffs, energy builders, escape moves, and even knock-backs that will throw your opponent in one of many specific directions so you can strategically plan your fighting flow. The escape moves allow the user to spend a large amount of stamina to get out of a sticky, outnumbered situation, or break the opponent's combo.
Beam lock battles have been removed from this game, which was a little disappointing at first, but the developers reasoned that this mechanic really offered nothing strategic to the gameplay, couldn't be effectively measured over network battles, and only served the purpose of WRECKING YOUR CONTROLLER.
Sure, you can play the game as a button-mashing free-for-all, but in the higher difficulties, you will find yourself frustrated unless you are willing to learn some of the finer points of the game, like effectively using your block to "just guard" (timing your blocks with your opponents' attacks to gain stamina) or back-punching when your opponent teleports behind you to break their combo.
Pair these customizable move options with all of the customizable, stat-boosting clothing options, character-selection options (even race and gender affect your stats), and online events, and this is easily the most robust DBZ fighting game I've played, especially when compared to Budokai Tenkaichi 3, which, at the time, seemed incredibly dense in terms of content and customizability.
Budokai Tenkaichi 3 may have had more advanced techniques built into the base fighting mechanics, like Dragon Rush and things like that, which had to be memorized in order to be used effectively (at least for me), but Xenoverse's system seems easy to pick up, and, due to it's huge flexibility, fun and engaging for a variety of player skill levels.
I am very pleasantly surprised.